Solve for y
y=10
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\sqrt{3y+51}=y+6-7
Subtract 7 from both sides of the equation.
\sqrt{3y+51}=y-1
Subtract 7 from 6 to get -1.
\left(\sqrt{3y+51}\right)^{2}=\left(y-1\right)^{2}
Square both sides of the equation.
3y+51=\left(y-1\right)^{2}
Calculate \sqrt{3y+51} to the power of 2 and get 3y+51.
3y+51=y^{2}-2y+1
Use binomial theorem \left(a-b\right)^{2}=a^{2}-2ab+b^{2} to expand \left(y-1\right)^{2}.
3y+51-y^{2}=-2y+1
Subtract y^{2} from both sides.
3y+51-y^{2}+2y=1
Add 2y to both sides.
5y+51-y^{2}=1
Combine 3y and 2y to get 5y.
5y+51-y^{2}-1=0
Subtract 1 from both sides.
5y+50-y^{2}=0
Subtract 1 from 51 to get 50.
-y^{2}+5y+50=0
Rearrange the polynomial to put it in standard form. Place the terms in order from highest to lowest power.
a+b=5 ab=-50=-50
To solve the equation, factor the left hand side by grouping. First, left hand side needs to be rewritten as -y^{2}+ay+by+50. To find a and b, set up a system to be solved.
-1,50 -2,25 -5,10
Since ab is negative, a and b have the opposite signs. Since a+b is positive, the positive number has greater absolute value than the negative. List all such integer pairs that give product -50.
-1+50=49 -2+25=23 -5+10=5
Calculate the sum for each pair.
a=10 b=-5
The solution is the pair that gives sum 5.
\left(-y^{2}+10y\right)+\left(-5y+50\right)
Rewrite -y^{2}+5y+50 as \left(-y^{2}+10y\right)+\left(-5y+50\right).
-y\left(y-10\right)-5\left(y-10\right)
Factor out -y in the first and -5 in the second group.
\left(y-10\right)\left(-y-5\right)
Factor out common term y-10 by using distributive property.
y=10 y=-5
To find equation solutions, solve y-10=0 and -y-5=0.
\sqrt{3\times 10+51}+7=10+6
Substitute 10 for y in the equation \sqrt{3y+51}+7=y+6.
16=16
Simplify. The value y=10 satisfies the equation.
\sqrt{3\left(-5\right)+51}+7=-5+6
Substitute -5 for y in the equation \sqrt{3y+51}+7=y+6.
13=1
Simplify. The value y=-5 does not satisfy the equation.
y=10
Equation \sqrt{3y+51}=y-1 has a unique solution.
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