Question 135
"a) If a quadrilateral $ABCD$ is such that $\angle ABC = \angle ADC = 90^\circ$, then $AB^2 - CD^2 = AD^2 - BC^2$."
b) "If a quadrilateral $ABCD$ is such that $\angle ACB = \angle ADC = 90^\circ$, then $AB^2 = BC^2 + CD^2 + AD^2$."
Prove these results.
b) "If a quadrilateral $ABCD$ is such that $\angle ACB = \angle ADC = 90^\circ$, then $AB^2 = BC^2 + CD^2 + AD^2$."
Prove these results.