Expand Using Pascal's Triangle (x+3)^7

${(x + 3)}^{7}$

Step 1

Pascal\'s Triangle can be displayed as such:

$1$

$1 - 1$

$1 - 2 - 1$

$\dots$

$1 - 5 - 10 - 10 - 5 - 1$

$1 - 6 - 15 - 20 - 15 - 6 - 1$

$1 - 7 - 21 - 35 - 35 - 21 - 7 - 1$

The triangle can be used to calculate the coefficients of the expansion of ${(a + b)}^{n}$ by taking the exponent $n$ and adding $1$ . The coefficients will correspond with line $n + 1$ of the triangle. For ${(x + 3)}^{7}$ , $n = 7$ so the coefficients of the expansion will correspond with line $8$ .

Step 2

The expansion follows the rule ${(a + b)}^{n} = c_{0} a^{n} b^{0} + c_{1} a^{n - 1} b^{1} + c_{n - 1} a^{1} b^{n - 1} + c_{n} a^{0} b^{n}$ . The values of the coefficients, from the triangle, are $1 - 7 - 21 - 35 - 35 - 21 - 7 - 1$ .

$1 a^{7} b^{0} + 7 a^{6} b + 21 a^{5} b^{2} + 35 a^{4} b^{3} + 35 a^{3} b^{4} + 21 a^{2} b^{5} + 7 a b^{6} + 1 a^{0} b^{7}$

Step 3

Substitute the actual values of $a$ $x$ and $b$ $3$ into the expression.

$1 {(x)}^{7} {(3)}^{0} + 7 {(x)}^{6} {(3)}^{1} + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Step 4

Simplify each term.

Multiply ${(x)}^{7}$ by $1$ .

${(x)}^{7} {(3)}^{0} + 7 {(x)}^{6} {(3)}^{1} + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Anything raised to $0$ is $1$ .

$x^{7} \cdot 1 + 7 {(x)}^{6} {(3)}^{1} + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $x^{7}$ by $1$ .

$x^{7} + 7 {(x)}^{6} {(3)}^{1} + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Evaluate the exponent.

$x^{7} + 7 x^{6} \cdot 3 + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $3$ by $7$ .

$x^{7} + 21 x^{6} + 21 {(x)}^{5} {(3)}^{2} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Raise $3$ to the power of $2$ .

$x^{7} + 21 x^{6} + 21 x^{5} \cdot 9 + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $9$ by $21$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 35 {(x)}^{4} {(3)}^{3} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Raise $3$ to the power of $3$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 35 x^{4} \cdot 27 + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $27$ by $35$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 35 {(x)}^{3} {(3)}^{4} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Raise $3$ to the power of $4$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 35 x^{3} \cdot 81 + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $81$ by $35$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 21 {(x)}^{2} {(3)}^{5} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Raise $3$ to the power of $5$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 21 x^{2} \cdot 243 + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Multiply $243$ by $21$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 7 {(x)}^{1} {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Simplify.

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 7 x {(3)}^{6} + 1 {(x)}^{0} {(3)}^{7}$

Raise $3$ to the power of $6$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 7 x \cdot 729 + 1 {(x)}^{0} {(3)}^{7}$

Multiply $729$ by $7$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 5103 x + 1 {(x)}^{0} {(3)}^{7}$

Multiply ${(x)}^{0}$ by $1$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 5103 x + {(x)}^{0} {(3)}^{7}$

Anything raised to $0$ is $1$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 5103 x + 1 {(3)}^{7}$

Multiply ${(3)}^{7}$ by $1$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 5103 x + {(3)}^{7}$

Raise $3$ to the power of $7$ .

$x^{7} + 21 x^{6} + 189 x^{5} + 945 x^{4} + 2835 x^{3} + 5103 x^{2} + 5103 x + 2187$

Expand Using Pascal's Triangle (x+3)^7

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