Posted by **Shayna** on Monday, October 3, 2011 at 11:49pm.

Explain how lim x->1 ((x^2)-1)/(sqrt(2x+2)-2) = 4

- Calculus -
**Reiny**, Tuesday, October 4, 2011 at 8:06am
Rationalize the denominator, that is, multiply top and bottom by √(2x+2) + 2 to give you

lim [(x^2 - 1)/(√(2x+2) - 2) ] * (√(2x+2) + 2)/(√(2x+2) + 2)

= (x+1)(x-1)(√(2x+2) + 2)/(2x+2 - 4)

= (x+1)(x-1)(√(2x+2) + 2)/( 2(x-1))

= lim (x+1)(√(2x+2) + 2)/2 as x --> 1

= 2(√4+2)/2 = 4

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