Answer:
A
Step-by-step explanation:
1.move -21 over to the other side to get x^2 - 10x +21
2. factor. you want to find something that multiples to 21 (the c value) but adds up to -10 (the b value.) the numbers are -7 and -3. so you would factor it out like this: (x-7)(x-3)
3. set each factor to 0 to find the x values
x-7=0 and x-3=0. once you move the numbers over to isolate the x term, you should get x=7 and x=3.
