Calculate: 9x^2-42xy+49y^2

Expression: $9{x}^{2}-42xy+49{y}^{2}$

Write the number in the exponential form with an exponent of $2$

${3}^{2}{x}^{2}-42xy+49{y}^{2}$

Write the expression as a product with the factors $3x$ and $7y$

${3}^{2}{x}^{2}-2 \times 3x \times 7y+49{y}^{2}$

Write the number in the exponential form with an exponent of $2$

${3}^{2}{x}^{2}-2 \times 3x \times 7y+{7}^{2}{y}^{2}$

Multiply the terms with equal exponents by multiplying their bases

${\left( 3x \right)}^{2}-2 \times 3x \times 7y+{7}^{2}{y}^{2}$

Multiply the terms with equal exponents by multiplying their bases

${\left( 3x \right)}^{2}-2 \times 3x \times 7y+{\left( 7y \right)}^{2}$

Use ${a}^{2}-2ab+{b}^{2}={\left( a-b \right)}^{2}$ to factor the expression

${\left( 3x-7y \right)}^{2}$