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 12 as well and sum (Inside, Outside) to equal 7. For this problem, those two numbers are 3 and 4. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² + 7y + 12
y² + (3 + 4)y + (3 x 4)
(y + 3)(y + 4)

The perimeter of a triangle is the sum of the lengths of its sides:

p = x + y + z
p = 6cm + 15cm + 15cm = 36cm

The formula for area is πr²:

a = πr²
a = π(5²)
a = 25π

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.

2a + 6a = 8a

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).