Algebra · real student question

Multiply using the rule for the square of a binomial: (4x² − 3)².

Question

Multiply using the rule for the square of a binomial:

(4x23)2(4x^2 - 3)^2

Step-by-step solution

  1. Recognise the pattern. The expression is a single binomial raised to the second power, so the shortcut (ab)2=a22ab+b2(a-b)^2 = a^2 - 2ab + b^2 applies. Matching terms gives a=4x2a = 4x^2 and b=3b = 3.

  2. Square the first term. a2=(4x2)2=42(x2)2=16x4a^2 = (4x^2)^2 = 4^2 \cdot (x^2)^2 = 16x^4. Both the coefficient and the power get squared — a common slip is to write 4x44x^4.

  3. Double the product of the two terms. 2ab=24x23=24x22ab = 2 \cdot 4x^2 \cdot 3 = 24x^2. Because the binomial has a minus sign, this middle term is subtracted.

  4. Square the last term. b2=32=9b^2 = 3^2 = 9. Squaring removes the sign, so the constant is positive even though the original term was 3-3.

  5. Assemble the trinomial. Putting the three pieces together in descending powers gives 16x424x2+916x^4 - 24x^2 + 9.

  6. Check with one value. At x=1x = 1 the original is (43)2=1(4-3)^2 = 1 and the expansion is 1624+9=116 - 24 + 9 = 1, so the two agree.

Answer

16x424x2+916x^4 - 24x^2 + 9

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