\(Đề:góc\text{ }SIS=30\text{°}\)

\(Vẽ\text{ }pháp\text{ }tuyến\text{ }IN\perp qua\text{ }gương\text{ }phẳng\text{ }G\)

\(nên\text{ }góc\text{ }GIN=90\text{°}\)

\(ta\text{ }có:\text{ }góc\text{ }GIS+i'=góc\text{ }GIN=90\text{°}\)

\(\rightarrow i=90\text{°}-góc\text{ }\text{ }GIS\)

\(\rightarrow i=90\text{°}-30\text{°}=60\text{°}\)

\(Theo\text{ }định\text{ }luật\text{ }phản\text{ }xạ\text{ }ánh\text{ }sáng\text{ }thì:i'=i=60\text{°}\)

\(Đáp\text{ }số:góc\text{ }phản\text{ }xạ:60\text{°}.\)

\(1424\text{×}59+42\text{×}1424-1424\)

\(=1424\text{×}59+42\text{×}1424-1424\text{×}1\)

\(=1424\text{×}\left(59+42-1\right)\)

\(=1424\text{×}100=142400\)

\(69,4:0,1-69,4:0,125-69,4\)

\(=69,4\text{×}10-69,4\text{×}8-69,4\text{×}1\)

\(=69,4\text{×}\left(10-8-1\right)\)

\(=69,4\text{×}1=69,4\)

\(223+4315-175=4363\)

\(6438-235\text{×}2=5968\)

\(480-120:4=450\)

\(63+24\text{×}3=135\)

\(-Số\text{ }chia\text{ }hết\text{ }cho\text{ }2:5968;450.\)

\(-Số\text{ }chia\text{ }hết\text{ }cho\text{ }5:450;135.\)

\(3.\left(25:5-14:2\right)-5.\left(6:2\right)\)

\(=3.\left(5-7\right)-5.3\)

\(=3.\left(-2\right)-5.3\)

\(=-6-15=-21\)

\(=28,17\)