Question

if the area of triangle A(a,2a) B(-2,6) C(3,1) is 10 sq.units find a

Answer 1

x1 = a        x2 = -2        x3 = 3

y1 = 2a       y2 = 6         y3 = 1

formula time!

1/2 { a+(6-1) + -2 ( 1- 2a) + 3 ( 2a - 6)} = 10

1/2 { 6a -a -2 + 4a + 6a -18 } = 10

1/2 {  15 a - 20 } = 10

taking 1/2 to the other side

15 a - 20 = 20

a = 40  / 15 = 8/3