Example

Multiplying (x+3)(x+7)(x + 3)(x + 7) Using the FOIL Method

Multiply (x+3)(x+7)(x + 3)(x + 7) using the FOIL method to systematically find all four products. Step 1 — First: Multiply the first terms of each binomial: xx=x2x \cdot x = x^2. Step 2 — Outer: Multiply the outermost terms: x7=7xx \cdot 7 = 7x. Step 3 — Inner: Multiply the innermost terms: 3x=3x3 \cdot x = 3x. Step 4 — Last: Multiply the last terms of each binomial: 37=213 \cdot 7 = 21. Writing these four products in sequence gives: x2+7x+3x+21x^2 + 7x + 3x + 21. Step 5 — Combine like terms: The Outer and Inner products, 7x7x and 3x3x, are like terms. Add their coefficients (7+3=107 + 3 = 10) to yield 10x10x. The final simplified trinomial is x2+10x+21x^2 + 10x + 21.

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Updated 2026-04-29

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