Question

Tính:

\(a)\left( {a - 3b} \right)\left( {a + 3b} \right)\)

\(b)\left( {2{\rm{x}} + 5} \right)\left( {2{\rm{x}} - 5} \right)\)

\(c)\left( {4y - 1} \right)\left( {4y + 1} \right)\)

Answer 1

\(a)\left( {a - 3b} \right)\left( {a + 3b} \right) = {a^2} - {\left( {3b} \right)^2} = {a^2} - 9{b^2}\)

\(b)\left( {2{\rm{x}} + 5} \right)\left( {2{\rm{x}} - 5} \right) = {\left( {2{\rm{x}}} \right)^2} - {5^2} = 4{{\rm{x}}^2} - 25\)

\(c)\left( {4y - 1} \right)\left( {4y + 1} \right) = {\left( {4y} \right)^2} - {1^2} = 16{y^2} - 1\)