The rectangle below has an area of x 2 + 1 1 x + 2 8 x 2 +11x+28x, start superscript, 2, end superscript, plus, 11, x, plus, 28 square meters and a length of x + 7 x+7x, plus, 7 meters.

1. ∠1 is complementary to ∠2 and ∠3 is complementary to ∠2. subtraction property of equality 2. m∠1 + m∠2 = 90 and m∠3 + m∠2 = 90 substitution 3. m∠1 + m∠2 = m∠3 + m∠2 definition of complementary 4. m∠1 = m∠3 given