1) the one making up the peak of the large triangle
2)the large triangle
are similar. That is because the 2 bases are parallel and corresponding angles are equal. The third angle at the peak is common. So by AAA they are similar.
Proportion
Therefore the sides are in proportion.
5/40 = 3/(2x + 10)
Solution
Cross multiply
5*(2x + 10) = 40*3
Remove the brackets on the left. Combine the right.
