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Answer:
∠ABD = 100°
∠CBD = x
we have to find the value of x .
Since ∠ABD & ∠CBD formed on straight line.
Then Sum of ∠ABD & ∠CBD is 180° ( by linear pair)
[tex] \dashrightarrow\sf \: 100 {}^{ \circ} + x \: = 180 {}^{ \circ} \\ \\ \dashrightarrow\sf \:x \: = 180 {}^{ \circ} - 100 {}^{ \circ} \\ \\ \dashrightarrow\sf \:x \: = 80 {}^{ \circ} [/tex]
So, the value of x is 80° .
♧ Supplementary angles add up to 180 degrees
x + 100 = 180
x = 180 - 100
Hope it helps ~