step 7
Find out AB in the right triangle ABC and CD in the right triangle ADC
Reason -----> by Pythagorean Theorem in a right triangle
step 8
AB=CD
because
AC^2=AB^2+BC^2
AB^2=AC^2-BC^2 -----> triangle ABC
AC^2=CD^2+AD^2
CD^2=AC^2-AD^2 -----> triangle ADC
Remember that
BC=AD -----> given
substitute
AB^2=AC^2-BC^2
CD^2=AC^2--BC^2
AB=CD
step 9
triangle ABC and triangle ADC are congruent by SSS