<span>If you have a quadratic equation in the form <span>a<span>x2</span>+bx+c</span>
</span>Step 1) Determine the product of AC (the coefficients in a quadratic equation)Step 2) Determine what factors of <span><span>a⋅c</span> sum to b</span>Step 3) "ungroup" the middle term to become the sum of the factors found in step 2Step 4) group the pairs.
<u>Let's take this problem step-by-step</u>:
<u>The ;unlabeled angle' adjacent to the 'outside angle of measure 78°'</u>
⇒ is on a straight line
⇒ sum of angle measure = 180 degrees

<u>Now we know:</u>
⇒ sum of all angles in a triangle ⇒ 180°
<u>Let's put that in equation form and solve:</u>

<u>Answer: 21°</u>
<u></u>
Hope that helps!
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Seventy-three is the answer