Question

Can someone please solve this.

Answer 1

Answer:

see explanation

Step-by-step explanation:

A

Given

(x² + 3)² + 21 = 10x² + 30 ← factor out 10 from each term on the right side

(x² + 3)² + 21 = 10(x² + 3) ← subtract 10(x² + 3) from both sides

(x² + 3)² - 10(x² + 3) + 21 = 0

Substituting u = x² + 3 into the equation gives

u² - 10u + 21 = 0 → D

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B

Using u² - 10u + 21 = 0 to solve the equation

Consider the factors of the constant term (+ 21) which sum to give the coefficient of the u- term (- 10)

The factors are - 3 and - 7, since

- 3 × - 7 = 21 and - 3 - 7 = - 10, thus

(u - 3)(u - 7) = 0

Equate each factor to zero and solve for u

u - 3 = 0 ⇒ u = 3

u - 7 = 0 ⇒ u = 7

We now have to use the substitution to convert the solutions into terms of x, that is

x² + 3 = 3 ( subtract 3 from both sides )

x² = 0 ⇒ x = 0 → D

x² + 3 = 7 ( subtract 3 from both sides )

x² = 4 ( take the square root of both sides )

x = ± $\sqrt{4}$ = ± 2

Thus x = - 2 → C

x = 2 → E