What is the area of the triangle formed by the lines 5 x − 2 y = 1 0 , 3 x + 4 y = 1 2 a n d x − a x i s ? Give answer till 2 digits after decimal point.
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To find the area you must know where the 3 points of the triangle lie:
Any line a x + b y = c intersects x-axis at a c , 0
Therefore 2 of the lines are ( 2 , 0 ) and ( 4 , 0 )
The third line lies at the intersection of 5 x − 2 y = 1 0 and 3 x + 4 y = 1 2 , that is it is the solution of these 2 equations
Solution of the equations: 3 x + 4 y = 1 2 5 x − 2 y = 1 0 Multiplying our last equation by 2 1 0 x − 4 y = 2 0 Adding this and our first equation 1 3 x = 3 2 x = 1 3 3 2 Put this in our first equation 3 ( 1 3 3 2 ) + 4 y = 1 2 1 3 9 6 + 4 y = 1 2 4 y = 1 2 − 1 3 9 6 y = 3 − 1 3 2 4 = 1 3 3 9 − 2 4 = 1 3 1 5
Now consider the line from ( 2 , 0 ) to ( 4 , 0 ) as the base of the triangle. Then the height will be the distance of ( 1 3 3 2 , 1 3 1 5 ) from the base and as the base is the x-axis the height is the ordinate of the point.
Therefore area= 2 1 ( 4 − 2 ) ( 1 3 1 5 ) = 1 3 1 5 = 1 . 1 5 3 8 4 6 1 5 . . . )
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Solving two equations at a time, we get these three points of intersection: ( 2 , 0 ) , ( 4 , 0 ) , ( 1 3 3 2 , 1 3 1 5 )
\[\begin{align} \text{Area }&= \frac{1}{2} \cdot b \cdot h \\ &= \frac{1}{2} \cdot(4-2)\cdot \bigg(\frac{15}{13} \bigg) \\ &= \frac{1}{\cancel{2}} \cdot(\cancel{2})\cdot \bigg(\frac{15}{13} \bigg) \\ &\approx \boxed{1.15}
\end{align}\]