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If x=3+22โ, then find the value of xโxโ1โ.
2โ
2
22โ
4
2
Recognize that 3+22โ is of the form (a+b)2=a2+b2+2ab, where a=2โ and b=1. Thus, xโ=2โ+1.
x=3+22โ
x=(2โ+1)2
Recognize that 3+22โ is of the form (a+b)2=a2+b2+2ab, where a=2โ and b=1. Thus, xโ=2โ+1.
Students often try to rationalize the denominator of xโxโ1โ without simplifying x first, leading to complex algebraic calculations.
Simplify the given value of x
Express x=3+22โ as a perfect square.
x=(2โ)2+12+2(2โ)(1)=(2โ+1)2
Calculate the square root of x
Taking the square root on both sides, we get the value of xโ.
xโ=(2โ+1)2โ=2โ+1
Substitute into the expression
Substitute x=3+22โ and xโ=2โ+1 into xโxโ1โ.
2โ+13+22โโ1โ=2โ+12+22โโ
Final simplification
Factor out 2 from the numerator to simplify.
2โ+12(1+2โ)โ=2
B is correct because the expression simplifies to 2 after substituting x=(2โ+1)2.
This technique of identifying perfect squares inside radicals is frequently used in trigonometric value simplification and competitive aptitude problems involving nested roots.