31.
If the slope of one of the lines represented by $$a{x^2} + 2hxy + b{y^2} = 0$$ is the square of the other, then $$\frac{{a + b}}{h} + \frac{{8{h^2}}}{{ab}} = ?$$
Let $$m$$ and $${m^2}$$ be the slopes of the lines represented by $$a{x^2} + 2hxy + b{y^2} = 0$$
Then, $$m + {m^2} = - \frac{{2h}}{b}$$ and $$m{m^2} = \frac{a}{b}{\text{ or }}{m^3} = \frac{a}{b}$$
$$\eqalign{
& \therefore \,{\left( {m + {m^2}} \right)^3} = {\left( { - \frac{{2h}}{b}} \right)^2} \cr
& \therefore \,{m^3} + {m^6} + 3m{m^2}\left( {m + {m^2}} \right) = - \frac{{8{h^3}}}{{{b^3}}} \cr
& \therefore \,\frac{a}{{{b^2}}}\left( {a + b} \right) + \frac{{8{h^3}}}{{{b^3}}} = \frac{{6ah}}{{{b^2}}} \cr
& \therefore \,\frac{{a + b}}{h} + \frac{{8{h^2}}}{{ab}} = 6 \cr} $$
These are the set of parallel lines and the distance between parallel lines are equal. So, the figure is a rhombus.
32.
Area of the parallelogram formed by the lines $$y = mx, \,y=mx+1, \,y=nx$$ and $$y=nx+1$$ equals-
A
$$\frac{{\left| {m + n} \right|}}{{{{\left( {m - n} \right)}^2}}}$$
B
$$\frac{2}{{\left| {m + n} \right|}}$$
C
$$\frac{1}{{\left( {\left| {m + n} \right|} \right)}}$$
D
$$\frac{1}{{\left( {\left| {m - n} \right|} \right)}}$$
Clearly from the figure, the image is the combined rays given by $$y = 1.\left( {x - 2} \right)$$ and $$y = - 1.\left( {x - 2} \right)$$ i.e., $$y = \left| {x - 2} \right|.$$
34.
The line $$L$$ given by $$\frac{x}{5} + \frac{y}{b} = 1$$ passes through the point (13, 32). The line $$K$$ is parallel to $$L$$ and has the equation $$\frac{x}{c} + \frac{y}{3} = 1.$$ Then the distance between $$L$$ and $$K$$ is-
Slope of line $$L = - \frac{b}{5}$$
Slope of line $$K = - \frac{3}{c}$$
Line $$L$$ is parallel to line $$k.$$
$$ \Rightarrow \frac{b}{5} = \frac{3}{c}\,\, \Rightarrow bc = 15$$
(13, 32) is a point on $$L.$$
$$\eqalign{
& \therefore \frac{{13}}{5} + \frac{{32}}{b} = 1 \cr
& \Rightarrow \frac{{32}}{b} = - \frac{8}{5} \cr
& \Rightarrow b = - 20 \cr
& \Rightarrow c = - \frac{3}{4} \cr} $$
Equation of $$K:\,\,\,\,\,\,y - 4x = 3 \Rightarrow 4x - y + 3 = 0$$
Distance between $$L$$ and $$K\,\,\, = \frac{{\left| {52 - 32 + 3} \right|}}{{\sqrt {17} }} = \frac{{23}}{{\sqrt {17} }}$$
35.
A ray of light passing through a point $$\left( {1,\,2} \right)$$ is reflected on the $$x$$-axis at point $$Q$$ and passes through the point $$\left( {5,\,8} \right).$$ Then the abscissa of the point $$Q$$ is :
Let point $$Q$$ be $$\left( {x,\,0} \right)$$
Since, $${m_{PQ}} = - {m_{RQ}}$$
therefore $$\frac{{0 - 2}}{{x - 1}} = - \left( {\frac{{8 - 0}}{{5 - x}}} \right) \Rightarrow x = \frac{9}{5}$$
36.
Let $$a, \,b, \,c$$ and $$d$$ be non-zero numbers. If the point of intersection of the lines $$4ax + 2ay + c=0$$ and $$5bx + 2by+ d=0$$ lies in the fourth quadrant and is equidistant from the two axes then-
Given lines are
$$4ax+2ay+c=0$$
$$5bx + 2by + d=0$$
The point of intersection will be
$$\eqalign{
& \frac{x}{{2ad - 2bc}} = \frac{{ - y}}{{4ad - 5bc}} = \frac{1}{{8ab - 10ab}} \cr
& \Rightarrow x = \frac{{2\left( {ad - bc} \right)}}{{ - 2ab}} = \frac{{bc - ad}}{{ad}} \cr
& \Rightarrow y = \frac{{5bc - 4ad}}{{ - 2ad}} = \frac{{4ad - 5bc}}{{2ab}} \cr} $$
$$\because $$ Point of intersection is in fourth quadrant so $$x$$ is positive and $$y$$ is negative.
Also distance from axes is same
So $$x=-y$$ ($$\because $$ distance from $$x$$-axis is $$-y$$ as $$y$$ is negative)
$$\eqalign{
& \frac{{bc - ad}}{{ab}} = \frac{{5bc - 4ad}}{{2ab}} \cr
& \Rightarrow \,\,3bc - 2ad = 0 \cr} $$
37.
The point $$P\left( {2,\,1} \right)$$ is shifted by $$3\sqrt 2 $$ parallel to the line $$x+y=1,$$ in the direction of increasing ordinate, to reach $$Q.$$ The image of $$Q$$ by the line $$x+y=1$$ is :
If a point is equidistant from the two intersecting lines, then the locus of this point is the angle bisector of those lines.
Now, let $$\left( {h,\,k} \right)$$ be the point which is equidistant from the lines $$4x - 3y + 7 = 0$$ and $$3x - 4y + 14 = 0$$
$$\eqalign{
& {\text{Then, }}\frac{{4h - 3k + 7}}{{\sqrt {{4^2} + {{\left( { - 3} \right)}^2}} }} = \pm \frac{{3h - 4k + 14}}{{\sqrt {{3^2} + {{\left( { - 4} \right)}^2}} }} \cr
& \Rightarrow 4h - 3k + 7 = \pm \left( {3h - 4k + 14} \right) \cr
& \Rightarrow h + k - 7 = 0{\text{ and }}7h - 7k + 21 = 0 \cr} $$
Hence locus of $$\left( {h,\,k} \right)$$ is $$x + y - 7 = 0$$ and $$x - y + 3 = 0.$$
39.
The lines $${L_1}:y - x = 0$$ and $${L_2}:2x + y = 0$$ intersect the line $${L_3}:y + 2 = 0$$ at $$P$$ and $$Q$$ respectively. The bisector of the acute angle between $${L_1}$$ and $${L_2}$$ intersects $${L_3}$$ at $$R.$$ Statement-1: The ratio $$PR : RQ$$ equals $$2\sqrt 2 :\sqrt 5 $$ Statement-2: In any triangle, bisector of an angle divides the triangle into two similar triangles.
A
Statement-1 is true, Statement-2 is true; Statement-2 is not a correct explanation for Statement-1.
B
Statement-1 is true, Statement-2 is false.
C
Statement-1 is false, Statement-2 is true.
D
Statement-1 is true, Statement-2 is true; Statement-2 is a correct explanation for Statement-1.
Answer :
Statement-1 is true, Statement-2 is false.
$$\eqalign{
& {L_1}:y - x = 0 \cr
& {L_2}:2x + y = 0 \cr
& {L_3}:y + 2 = 0 \cr} $$
On solving the equation of line $${L_1}$$ and $${L_2}$$ we get their point of intersection (0, 0) i.e., origin $$O.$$
On solving the equation of line $${L_1}$$ and $${L_3},$$
we get $$P = \left( { - 2,\, - 2} \right)$$
Similarly, we get $$Q = \left( { - 1,\, - 2} \right)$$
We know that bisector of an angle of a triangle, divide the opposite side the triangle in the ratio of the sides including the angle [ Angle Bisector Theorem of a Triangle ]
$$\therefore \frac{{PR}}{{RQ}} = \frac{{OP}}{{OQ}} = \frac{{\sqrt {{{\left( { - 2} \right)}^2} + {{\left( { - 2} \right)}^2}} }}{{\sqrt {{{\left( { - 1} \right)}^2} + {{\left( { - 2} \right)}^2}} }} = \frac{{2\sqrt 2 }}{{\sqrt 5 }}$$
40.
Let $$A (h, \,k), \,B(1, \,1)$$ and $$C (2, \,1)$$ be the vertices of a right angled triangle with $$AC$$ as its hypotenuse. If the area of the triangle is 1 square unit, then the set of values which $$'k\,'$$ can take is given by-