. If a + b = 10, what are two possible values for c that satisfy the equation below? (ax – 4)(bx + 5) = 21x2 + cx – 20
I need help answer pleas

check the picture below.

well, the angle at the vertex d is clearly not a right-angle, let's check for the one at the vertex f which does look like,   however if it's indeed, that means ef is perpendicular to df, in which case their slopes will be negative reciprocal of each other.

so the negative reciprocal of the slope of ef is 1, however the slope of df is not 1, is 1/2, so nope, they're not perpendicular lines.

i think c. but don't trust it.

step-by-step explanation:

m∠a is 90°

m∠b is 40°

cross multiplying, we get :

⇒ (3) × (5) = (9) × (x)

⇒ 15 = 9x