Chapter 6 - Systems of Equations and Inequalities - 6-2 Solving Systems Using Substitution - Practice and Problem-Solving Exercises - Page 371: 25

$x+y = 90$ $x = 4y$ $x=72$ degrees, $y=18$ degrees

A right triangle has three angles, one of which is 90 degrees. The other two degrees must equal 90 degrees. ($x+y = 90$) One angle is four times the other angle ($x=4y$) $x+y=90$ $4y + y = 90$ $5y= 90$ $5y/5 = 90/5$ $y=18$ $x=4y$ $x=4*18$ $x=72$