Line p is parallel to line q. Which proof explains why the sun of the interior angles of the triangle must be 180

We consider a triangle ABC as attached in the answer.

We draw a line parallel to AB that passes  through point C.

Angles C and C' are vertical angles,  therefore ∠C = ∠C'.  

Angles B and B' are corresponding angles,  therefore ∠B = ∠B'.

Angles A and A' are corresponding angles, therefore ∠A = ∠A'.

it can be seen that angle sum ∠A + ∠B + ∠C is equal to the angle sum ∠A' + ∠B' + ∠C'.

The three angles A', B', and C' form together a straight angle  so, their angle sum is 180°. But then the angle sum ∠A + ∠B + ∠C must also be 180°.

This proofs that sum of angles of a triangle is equal to 180.

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step-by-step explanation:

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answer:

25x^2 + 90x + 84

discussion:

mn(x) = m(n(x)) = m( 5x + 9) =

(5x + 9)^2 + 3 =>

25x^2 + 90x + 9^2 + 3 =

25x^2 + 90x + 84                 (as 9^2 = 9*9 = 81)

which is the second choice

regards,  

mrb

p.s.   i'll be on vacation from friday, dec 22 to jan 2, 2019. have a great new year!