Answer
$x = 1$
Work Step by Step
Theorem 6-20 states that in an isosceles trapezoid, diagonals are congruent. Let's set the two diagonals equal to one another:
$QS = RP$
Let's plug in the expressions for each diagonal:
$x + 5 = 3x + 3$
Subtract $5$ from each side of the equation to move constants to the right side of the equation:
$x = 3x - 2$
Subtract $3x$ from each side of the equation to move the variable to the left side of the equation:
$-2x = -2$
Divide each side by $-2$ to solve for $x$:
$x = 1$
