How do you answer this question?

enter image source here

2 Answers
May 1, 2018

#DeltaADC# is an isosceles right triangle

#:.#

#angleADC = 45^@#

#angleACB = 60^@# because is it one of the 3 angles of an equilateral triangle.

#:.#

#angleDCB = 90^@+60^@ = 150^@#

Because #angleBDC# is opposite one of two equal sides of #Delta BDC#:

#angleBDC = (180^@-angleDCB)/2#

#angleBDC = (180^@-150^@)/2#

#angleBDC = 15^@#

#angle ADB = angle ADC - angleBDC#

#angle ADB = 45^@ - 15^@#

#angle ADB = 30^@# Q.E.D.

May 1, 2018

.

Explanation:

enter image source here