Áp dụng BĐT BCS, ta có:
\(\left(2x+3y\right)^2\le\left(x^2+y^2\right)\left(2^2+3^2\right)\)
\(\left(2x+3y\right)^2\le52.\left(2^2+3^2\right)\)
\(\left(2x+3y\right)^2\le676\)
\(\left|2x+3y\right|\le26\)
Dấu ''='' xảy ra khi ...................... bận