To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -15 as well and sum (Inside, Outside) to equal 2. For this problem, those two numbers are -3 and 5. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 2y - 15
y² + (-3 + 5)y + (-3 x 5)
(y - 3)(y + 5)

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

Perimeter is equal to the sum of the four sides:

p = a + b + c + d
p = 7 + 9 + 6 + 4
p = 26

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

7a + 6a = 13a

According to the Pythagorean theorem, the hypotenuse squared is equal to the sum of the two perpendicular sides squared:

c² = a² + b²
c² = 8² + 2²
c² = 64 + 4
c² = 68
c = \( \sqrt{68} \)