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:

$$\left(\dfrac{-3}{26}\right)\cdot\left(\dfrac{-15}{19}\right)-\dfrac2{19}\cdot\left(\dfrac{-3}{26}\right)$$

$$=\dfrac3{26}\cdot\dfrac{15}{19}+\dfrac2{19}\cdot\dfrac3{26}$$

$$=\dfrac3{26}\cdot\left(\dfrac{15}{19}+\dfrac2{19}\right)$$

$$=\dfrac3{26}\cdot\dfrac{17}{19}$$

$$=\dfrac{51}{494}$$