Question 639002: Please help me solve this equation: this is factor completely Found 2 solutions by Susmitha, tam144:Answer by Susmitha(21) (Show Source):
You can put this solution on YOUR website! i hope you would like to find the value of x
x^2+8x-9=0
x^2+9x-x-9=0
x(x+9)-1(x+9)=0
(x+9)(x-1)=0
x=-9; x=1
both the values satisfy the above equation
You can put this solution on YOUR website! Solve x^2 + 8x - 9 = 0.
There are 2 Tips you should know when you meet this special type of quadratic equation. The standard form of a quadratic equation is: ax^2 + bx + c = 0.
Tip 1. When a + b + c = 0, one real root is x1 = 1 and the other x2 = c/a.
Example 1. Solve x^2 + 8x - 9 = 0. You see that a + b + c = 1 + 8 - 9 = 0. This is Tip 1. One real root is x1 = 1 and the other x2 = c/a = -9/1 = -9.
Example 2. Solve 7x^2 - 15x + 8 = 0. You find 7 - 15 + 8 = 0. This is Tip 1. The 2 real roots are: x1 = 1 and x2 = c/a = 8/7.
TIP 2. When a - b + c = 1, one real root x1 = -1 and the other x2 = -c/a.
Example 3. Solve 3x^2 - 5x - 8 = 0. You find 3 -(-5) - 8 = 0. This is Tip 2. Then one real root x1 = -1 and the other x2 = -c/a = 8/1 = 8.
Example 4. Solve 5x^2 + 17x + 12 = 0 . You find 5 -(17) + 12 = 0. Then x1 = -1 and x2 = -c/a = -12/5.
I advise you to remember these 2 Tips. It will save you a lot of time in solving quadratic equations.
Or, you can solve the given equation x^2 + 8x - 9 = 0 by the popular factoring method. Find 2 numbers whose product is -9 and whose sum is 8. Proceed: (-1, 9),(1, -9)OK. Factor the equation: x^2 + 8x - 9 = (x - 1)(x + 9) = 0.
Next, solve the 2 binomials for x.
x - 1 = 0 --> x = 1 and (x + 9) = 0 --> x = -9.
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