The coefficient of t²s⁵ in the expansion of (2t + s)⁷ is d. 84
What is binomial expansion?
Binomial expansion is the expansion of two term expressions such as (a + b)ⁿ where n is a rational number.
What is Pascal's triangle?
Pascal's triangle is atriangle used in determining the coefficients of a binomial expansion.
What is the coefficient of t²s⁵ in the expansion of (2t + s)⁷?
The general term for the expansion (a + b)ⁿ = ∑ⁿCₓaˣbⁿ⁻ˣ.
So, each term is ⁿCₓaˣbⁿ⁻ˣ.
Comparing (a + b)ⁿ with (2t + s)⁷,
So, its general term is ⁿCₓ(2t)ˣsⁿ⁻ˣ = ⁷Cₓ(2t)ˣsⁿ⁻ˣ
= ⁷Cₓ(2)ˣtˣsⁿ⁻ˣ
So, the coefficient term is ⁷Cₓ(2)ˣ
Now for the term t²s⁵, x = 2.
So, the coeficient term is ⁷Cₓ(2)ˣ = ⁷C₂(2)²
= 7!/2!(7 - 2)! × 4
= 7!/2!5! × 4
= 7 × 6 × 5!/(2! × 5!) × 4
= 7 × 6/2 × 4
= 7 × 3 × 4
= 84
So, the coefficient of t²s⁵ in the expansion of (2t + s)⁷ is d. 84
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