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The sum of all possible values of xx satisfying the equations 24x2−22x2+x+16+22x+30=02^{4 x^{2}}-2^{2 x^{2}+x+16}+2^{2 x+30}=0, is

Solution

✅ Correct Option: 3

We need to find all possible values of xx that satisfy:

24x2−22x2+x+16+22x+30=02^{4x^2} - 2^{2x^2 + x + 16} + 2^{2x + 30} = 0

This looks complicated, but there's a beautiful pattern hidden here.


Let's break down each term using exponent rules:

For the first term: 24x2=22⋅2x2=(22x2)22^{4x^2} = 2^{2 \cdot 2x^2} = (2^{2x^2})^2

For the middle term: 22x2+x+16=22x2⋅2x+162^{2x^2 + x + 16} = 2^{2x^2} \cdot 2^{x + 16}

For the last term: 22x+30=22x⋅2302^{2x + 30} = 2^{2x} \cdot 2^{30}

Key insight: We can rewrite 22x+302^{2x + 30} as (2x+15)2(2^{x + 15})^2 because 2x+30=2(x+15)2x + 30 = 2(x + 15)


Let's substitute our rewritten terms. Notice that x+16=(x+15)+1x + 16 = (x + 15) + 1, so:

22x2+x+16=22x2⋅2x+15⋅21=2⋅22x2⋅2x+152^{2x^2 + x + 16} = 2^{2x^2} \cdot 2^{x + 15} \cdot 2^1 = 2 \cdot 2^{2x^2} \cdot 2^{x + 15}

Our equation becomes:

(22x2)2−2⋅22x2⋅2x+15+(2x+15)2=0(2^{2x^2})^2 - 2 \cdot 2^{2x^2} \cdot 2^{x + 15} + (2^{x + 15})^2 = 0

This is a perfect square! Remember the formula: a2−2ab+b2=(a−b)2a^2 - 2ab + b^2 = (a - b)^2

Here, a=22x2a = 2^{2x^2} and b=2x+15b = 2^{x + 15}


Our equation becomes:

(22x2−2x+15)2=0(2^{2x^2} - 2^{x + 15})^2 = 0

Important property: If any number squared equals zero, then that number itself must be zero.

Therefore: 22x2−2x+15=02^{2x^2} - 2^{x + 15} = 0

This gives us: 22x2=2x+152^{2x^2} = 2^{x + 15}


When we have 2a=2b2^a = 2^b, then a=ba = b (since exponential functions are one-to-one).

So: 2x2=x+152x^2 = x + 15

2x2−x−15=02x^2 - x - 15 = 0


We need to factor 2x2−x−15=02x^2 - x - 15 = 0

We need two numbers that multiply to (2)(−15)=−30(2)(-15) = -30 and add to −1-1. Those numbers are −6-6 and +5+5 (since −6×5=−30-6 \times 5 = -30 and −6+5=−1-6 + 5 = -1)

2x2−x−15=2x2−6x+5x−152x^2 - x - 15 = 2x^2 - 6x + 5x - 15

2x(x−3)+5(x−3)=(2x+5)(x−3)=02x(x - 3) + 5(x - 3) = (2x + 5)(x - 3) = 0

Solutions: 2x+5=02x + 5 = 0 or x−3=0x - 3 = 0

Therefore: x=−52x = -\tfrac{5}{2} or x=3x = 3


The sum of all possible values is:

−52+3=−52+62=12-\tfrac{5}{2} + 3 = -\tfrac{5}{2} + \tfrac{6}{2} = \tfrac{1}{2}

Answer: 12\tfrac{1}{2}

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