Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

You need to find the value of a so solve the first equation in terms of x:

-8a + x = -4
x = -4 + 8a

then substitute the result (-4 - -8a) into the second equation:

4a - 7(-4 + 8a) = 9
4a + (-7 x -4) + (-7 x 8a) = 9
4a + 28 - 56a = 9
4a - 56a = 9 - 28
-52a = -19
a = \( \frac{-19}{-52} \)
a = \(\frac{19}{52}\)

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.

7a⁴ + 2a⁴ = 9a⁴

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).