Giải thích các bước giải:
a.Ta có:
$$\left(\dfrac12\right)^2-\dfrac38:\left(\dfrac{-9}2\right)$$
$$=\dfrac14-\dfrac38\cdot\dfrac{2}{-9}$$
$$=\dfrac14+\dfrac6{72}$$
$$=\dfrac13$$
b.Ta có:
$$\left(\dfrac{-4}{12}\right)-[\left(\dfrac{-13}{39}\right)-0.25]+0.75$$
$$=-\dfrac13-\left(-\dfrac13-0.25\right)+0.75$$
$$=-\dfrac13+\dfrac13+0.25+0.75$$
$$=0+1$$
$$=1$$
c.Ta có:
$$\left(\dfrac{-4}5\right)+18\cdot\left(\dfrac{-1}3\right)^2$$
$$=-\dfrac45+18\cdot\dfrac19$$
$$=-\dfrac45+2$$
$$=\dfrac65$$
d.Ta có:
$$\left(\dfrac{-3}{26}\right)\cdot\left(\dfrac{-15}{19}\right)-\dfrac2{19}\cdot\left(\dfrac{-3}{26}\right)$$
$$=\dfrac3{26}\cdot\dfrac{15}{19}+\dfrac2{19}\cdot\dfrac3{26}$$
$$=\dfrac3{26}\cdot\left(\dfrac{15}{19}+\dfrac2{19}\right)$$
$$=\dfrac3{26}\cdot\dfrac{17}{19}$$
$$=\dfrac{51}{494}$$