Square root??
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In this case, get rid of the +√5 in (-2+√5), we will multiply the conjugate of (-2+√5) which is (-2-√5) to cancel out the square root.
(-2+√5)(-2-√5) >>> FOIL method.
4 + 2√5 – 2√5 – √25 >>> 2√5 – 2√5 = 0
4 – √25
4 – 5
-1
The denominator is now -1
Remember when you multiply the denominator (bottom) by something, you will have to multiply the same thing to the numerator (top)
(1+√5)(-2-√5)
-2 -√5- 2√5- 5 >>> -√5is the same thing as -1√5, rewrite
-2 – 1√5- 2√5- 5 >>> Combine like terms, – 1√5and – 2√5
-2 – 3√5 – 5 >>> Combine like terms, -2 and -5
-7 – 3√ 5
The numerator is now -7 – 3√ 5
Now you have -7 – 3√ 5 / -1
Multiply both top and bottom by -1 (or -1/1) to cancel out the -1 on the bottom of -7 – 3√ 5 / -1
Top: (-7 – 3√ 5)(-1) = 7 + 3√ 5
Bottom: (-1)(-1) = 1
7 + 3√ 5/1 is the same thing as 7 + 3√ 5.
multiply the numerator and the denominator by (-2 – sqrt(5)) “the conjugate of the denominator:
numerator becomes: (1+sqrt(5)) * (-2-sqrt(5)) = 1*-2 – 1*sqrt(5)
-2*sqrt(5) – sqrt(5)*sqrt(5) = -2 -sqrt(5) -2 sqrt(5) – 5 =
-7 – 3sqrt(5)
denominator becomes: ( -2 + sqrt(5)) * ( -2 – sqrt(5)) =
-2*-2 + 2 * sqrt(5) – 2 * sqrt(5) – sqrt(5)*sqrt(5) = 4 – 5 = -1
numerator/denominator = ( -7 – 3sqrt(5)) /( -1) =
(-7)/(-1) – 3sqrt(5)/(-1) = 7 + 3 sqrt(5)
Thanks