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Question 83
The real root of the equation $$2^{6x} + 2^{3x + 2} - 21 = 0$$ is
Solution
Let $$2^{3x}$$ = v
$$2^{6x} + 2^{3x + 2} - 21 = 0$$
= $$v^2+4v-21=0$$
=(v+7)(v-3)=0
v=3, -7
$$2^{3x}$$ = 3 or $$2^{3x}$$ = -7(This can be negated)
3x=$$\log_23$$
x=$$\log_23$$/3
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