ta có : \(x^2-8x+16=\left(x-4\right)^2\ge0\)

\(\Rightarrow\) bất phương trình \(x^2-8x+16< 0\) vô nghiệm

4,25ngay=102gio

7,75gio=465phut

35gio=2100phut

12,5phut=750giay

33giay=0,55phut

ta có : \(\left(20^2+18^2+16^2+...+4^2+2^2\right)-\left(19^2+17^2+15^2+...+3^2+1^2\right)\)

\(=20^2-19^2+18^2-17^2+...+2^2-1^2\)

\(=\left(20^2-1^2\right)-\left(19^2-2^2\right)+\left(18^2-3^2\right)-...-\left(11^2-10^2\right)\)

\(=21.\left(20-1\right)-21\left(19-2\right)+21\left(18-3\right)-...-21\left(11-10\right)\)

\(=21.19-21.17+21.15-...-21.1\)

\(=21\left(19-17+15-13+...+3-1\right)\)

\(=21\left(2+2+...+2\right)=21.2.5=210\)

ta có : \(100^2-99^2+98^2-97^2+...+2^2-1^2\)

\(=\left(100^2-1^2\right)-\left(99^2-2^2\right)+\left(98^2-3^2\right)-...+\left(52^2-49^2\right)-\left(51^2-50^2\right)\)

\(=101\left(100-1\right)-101\left(99-2\right)+101\left(98-3\right)-...+101\left(52-49\right)-101\left(51-50\right)\)

\(=101.99-101.97+101.95-...+101.3-101.1\)

\(=101\left(99-97+95-93+...+3-1\right)\)

\(=101.\left(2+2+2+...+2\right)=101.2.25=5050\)

ta có : \(\left(2cosx-1\right)\left(sinx+cosx\right)=1\)

\(\Leftrightarrow2cosx.sinx+2cos^2x-1=sinx+cosx\)

\(\Leftrightarrow sin2x+cos2x=sinx+cosx\)

\(\Rightarrow2x=x\Leftrightarrow x=0\) vậy \(x=0\)

a,989898/454545 - 31313131/15151515

=98x10101/45x10101-31x1010101/15x1010101

=98/45-31/15=98/45-93/45=5/45=1/9

1 giờ 12 phút - 20 phút = 52 phút

nguoi 1: 69

nguoi 2: 356

10000 bạn ạ