Triangle Formed By Axes

Geometry Level 1

Find the equation of the line which has a slope of 3 4 -\frac{3}{4} and forms a triangle with the positive coordinate axes such that the triangle has an area of 24 square units.

3 x + 4 y + 24 = 0 3x + 4y + 24 = 0 4 x + 3 y 24 = 0 4x + 3y - 24 = 0 4 x + 3 y + 24 = 0 4x + 3y + 24 = 0 3 x + 4 y 24 = 0 3x + 4y - 24 = 0

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2 solutions

Anubhav Sharma
Mar 31, 2015

Hence, 3x + 4y + 24 = 0 and 3x + 4y - 24 = 0 are equation of straight line

The Answer would be only 3x+4y-24=0 as the question states The line forms triangle with the positive axes only .

Julie Das - 1 year, 9 months ago

t a n ɸ = s l o p e = 3 4 tan ɸ = slope = \frac{-3}{4} , since the slope is negative the line is inclined downwards to the right. We know that t a n ɸ tan ɸ is equal to o p p o s i t e s i d e a d j a c e n t s i d e \frac{opposite side}{adjacent side} . We can disregard the negative sign of the slope.

t a n ɸ = tan ɸ= y x = \frac{y}{x}= 3 4 \frac{3}{4} . We see that x = x= 4 3 y \frac{4}{3}y

A = A= 1 2 x y \frac{1}{2}xy

24 = 24= 1 2 \frac{1}{2} 4 3 y ( y ) \frac{4}{3}y(y)

From here,

y 2 = 36 y^2=36

y = 6 y=6 , we consider only the positive value.

Solving for x, we have

x = x= 4 3 ( 6 ) = 8 \frac{4}{3}(6)=8

So the intercepts are ( 0 , 6 ) (0,6) and ( 8 , 0 ) (8,0) .

From point-slope form of an equation of a line, we have

y y 1 = m ( x x 1 ) y-y_1=m(x-x_1)

y 0 = y-0= 3 4 ( x 8 ) \frac{-3}{4}(x-8)

4 y = 3 x + 24 4y=-3x+24

3 x + 4 y 24 = 0 3x+4y-24=0

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