How do you solve $3x^2 + 10x = 8$ by completing the square?

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Answer 1 · 2016-05-12T21:22:48

$x=2/3$ or $x=-4$

Multiply by $3$ and add $25$ to both sides to get:

$9x^2+30x+25=24+25$

which simplifies to:

$(3x+5)^2 = 49 = 7^2$

So $(3x+5)$ is a square root of $7^2$ , so it must be $7$ or $-7$ :

$3x+5 = +-7$

If $3x+5 = 7$ , then $3x=2$ , so $x=2/3$

If $3x+5 = -7$ , then $3x=-12$ , so $x=-4$

How do you solve 3x^2 + 10x = 83x^2 + 10x = 8 by completing the square?