Answer:
The valid value of x is x=-2
Step-by-step explanation:
we know that
The sum of the interior angles of any quadrilateral must be equal to 360 degrees
so
solve for x
Combine like terms
Divide by 10 both sides
The formula to solve a quadratic equation of the form
is equal to
in this problem we have
so
substitute in the formula
Remember that
The measure of the interior angle cannot be a negative number
For x=9
we have that the measure of one interior angle of quadrilateral is
substitute the value of x
therefore
The value of x=9 cannot be a solution
For x=-2
The measure of the interior angles are
therefore
The valid value of x is x=-2