Question

answer question number 17 a

Answer 1

this is type of quadiratral .
in ABCD
angle ABC + angle ADC +angle BAD +angle BCD =360 ------------(1)

also ,
Angle ADC (inner ) +angle ADC (external ) =360
angle ADC (external )=360 - x -----------(2)

now,
by equation (1)
beta + (360 -x ) + alpha + gama =360


{ from equation (1) angle ADC =360 -x

alpha + beta + gama = x
hence proved