Answer:
0-4 should go up to 1 5-9 should go up to 3 10-14 should go up to 4 15-19 should go up to 5 20-14 should go up to 2
Step-by-step explanation:
Hope this helps!
First we note symmetry in the expression's coefficients.
We also note that 7*3=21, and 7+3=10.
From the rational roots theorem, we are tempted to try with 3 and 7 as coefficients of the factors.
Try
(7b+3)(3b+7)=21b^2+(49+9)b+21
By switching the sign of 3b+7 to 3b-7, we get the signs right, to check:
(7b+3)(3b-7)=21b^2+(9-49)b-21=21b^2-40b-21 ....right!
So
(7b+3)(3b-7)=21b^2-40b-21
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x equals the square root of 18.