Question

Tính nhanh :1954²+21²−25²+42.1954

Answer 1

\(1954^2+21^2-25^2+42.1954\)

=\(1954^2+2.1954.21+21^2-25^2\)

=\(\left(1954+21\right)^2-25^2\)

=\(1975^2-25^2\)

=\(\left(1975+25\right)\left(1975-25\right)\)

=\(2000.1950\)

=3900000

Answer 2

\(\left(1954^2+2.21.1954+21^2\right)-25^2\)

\(=\left(1954+21\right)^2-25^2\)

\(=1975^2-25^2=\left(1975+25\right)\left(1975-25\right)=2000.1950=3900000\)

Answer 3

\(1954^2+21^2-25^2+42.1954\)

=\(\left(1960-6\right)^2+\left(21-25\right)\left(21+25\right)+\left(40+2\right)\left(1954\right)\)

=\(1960^2-2.6.1960+36-4.46+40.1954+2.1954\)

=3841600-23520+36-184+78160+3908

=3900000