A line on the coordinate grid can be defined by a slope-intercept equation: y = mx + b. For a given value of x, the value of y can be determined given the slope (m) and y-intercept (b) of the line. The slope of a line is change in y over change in x, \({\Delta y \over \Delta x}\), and the y-intercept is the y-coordinate where the line crosses the vertical y-axis.

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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

-9b + x = -4
x = -4 + 9b

then substitute the result (-4 - -9b) into the second equation:

-7b + 7(-4 + 9b) = 7
-7b + (7 x -4) + (7 x 9b) = 7
-7b - 28 + 63b = 7
-7b + 63b = 7 + 28
56b = 35
b = \( \frac{35}{56} \)
b = \(\frac{5}{8}\)

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.

8a - 8a = 0a

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.