February 02nd, 2015

2/2/2015

2 Comments

Test on using the Quadratic Formula 8.2.

Used Quadratic equations to solve problems Section 8.3

2 Comments

18/4/2015 06:05:19 am

How would you solve the equation (x+5)2 =81

N.B: 2 means squared.

Thanks

Mr R

18/4/2015 07:34:17 am

There are two ways:

Method 1:You would expand the LHS.
(x+5)^2 = (x+5)(x+5)= x(x+5) +5(x+5) = x^2 +5x +5x +25 = x^2 +10x +25

So LHS = RHS
x^2 +10x + 25 = 81 ( now solve this quadratic)
x^2 + 10x - 56 = 0
(x + 14)(x -4) = 0
So x= -14 or x= 4

Method 2: square root both sides but be careful because we must remember that there is both a + and - answer!

If (x +5)^2 = 81
Then x +5 = +9 or x +5 = -9
So x = 4 or x = -14

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Mr Roche

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February 02nd, 2015

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