supplementary angles add up to 180°.
x = measure of such angle
x + 20 = measure of her sibling.
since "x" has 20 less than her sibling, then clearly her sibling has to have 20 more than "x".

The answer of the next term is 31
A parallelogram is a figure which has its <em>opposite</em> sides to be <u>equal</u> and <u>parallel</u>. The <em>missing</em> reason in the proof is:
B. Substitution Angle Angle Postulate.
A <em>parallelogram</em> is a type of quadrilateral that has its <u>opposite</u> sides to be equal and parallel. The sum of its <em>internal</em> angles is
.
To <u>prove</u> that ∠ BAD ≅ ∠ DCB, we have:
Given parallelogram ABCD;
<BAC ≅ <ACD (alternate angle theorem)
<DAC ≅ <ACB (alternate angle theorem)
<BAC + <DAC = <BAD
Also,
<BCA + <DCA = <BCD
Therefore,
<BAD ≅ <DCB (Substitution Angle Angle Postulate)
Thus, the <u>missing</u> reason in the partial proof is:
option B. Substitution Angle Angle Postulate
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