1,Tính giá trị biểu thức:
a, A=\(\dfrac{7}{35}+\left(-1\dfrac{3}{4}+\dfrac{12}{7}\right)-\left(\dfrac{1}{4}-\dfrac{2}{7}-\dfrac{13}{35}\right)-\dfrac{3}{7}\)
b, B=\(\sqrt{\dfrac{25}{16}-}\dfrac{\left(-3\right)^2}{\left|-4\right|}+\dfrac{\sqrt{\left(-7\right)^2}}{4}-3.\left(\dfrac{5}{2}\right)^2\)