# How do you find the x and y intercept of 7x + 3y = –21?

Feb 25, 2017

See the entire solution process below:

#### Explanation:

To find the $x$ intercept by substitution you substitute $0$ for $y$ and solve for $x$:

$7 x + 3 y = - 21$ becomes:

$7 x + \left(3 \times 0\right) = - 21$

$7 x + 0 = - 21$

$7 x = - 21$

$\frac{7 x}{\textcolor{red}{7}} = - \frac{21}{\textcolor{red}{7}}$

$\frac{\textcolor{red}{\cancel{\textcolor{b l a c k}{7}}} x}{\cancel{\textcolor{red}{7}}} = - 3$

$x = - 3$ so the x-intercept is $- 3$ or $\left(- 3 , 0\right)$

To find the $y$ intercept by substitution you substitute $0$ for $x$ and solve for $y$:

$7 x + 3 y = - 21$ becomes:

$\left(7 \times 0\right) + 3 y = - 21$

$0 + 3 y = - 21$

$3 y = - 21$

$\frac{3 y}{\textcolor{red}{3}} = - \frac{21}{\textcolor{red}{3}}$

$\frac{\textcolor{red}{\cancel{\textcolor{b l a c k}{3}}} y}{\cancel{\textcolor{red}{3}}} = - 7$

$y = - 7$ so the y-intercept is $- 7$ or $\left(0 , - 7\right)$