a) S hình thoi là:
(19 x 12) : 2 = 114(cm2)
b) S hình thoi là;
(30 x 7) : 2 = 105(cm2)
\(1,\left(30\right)=1+\frac{30}{99}=1+\frac{10}{33}=\frac{43}{33}.\)
\(1,\left(30\right)=1+0,\left(30\right)=1+\frac{10}{33}=\frac{43}{33}.\)
\(1,\left(30\right)=1+\frac{30}{99}=\frac{43}{99}\)
Đặt x = 1,(30) thì 100x = 130,(30) => 100x - x = 130,(30) - 1,(30) <=> 99x = 129 => x = \(\frac{129}{99}=\frac{43}{33}\)