\(\dfrac{2}{7x9}+\dfrac{2}{9x11}+.......+\dfrac{2}{19+21}\)

Tính Nhanh:

X x 3,9 + X : 10 = 2,4

1. \(25\dfrac{1}{7}:\left(-\dfrac{5}{7}\right)-15\dfrac{1}{7}:\left(-\dfrac{5}{7}\right)+\dfrac{4}{5}\)            3.  \(2\dfrac{2}{3}:\left\{\left[\left(3,72-0.02\right)\dfrac{10}{37}\right]:\dfrac{5}{6}+2,8\right\}-\dfrac{7}{15}\)

2. \(\left(3+\dfrac{4}{5}-\dfrac{5}{12}\right)\left(\dfrac{6}{7}-\dfrac{3}{5}\right)^2\)

4.2³+3.\(\left(-\dfrac{1}{2}\right)^2\)-2².4+\(\left[\left(-2\right)^2:\dfrac{1}{2}\right]\)

Thực hiện phép tính:

a,\(\sqrt{25-9}\)        b,\(\sqrt{0,01}-\sqrt{0,25}\)

c,\(\sqrt{2.2^2+4^2+5^2}\)

Tìm x biết:

a, \(\sqrt{x-1}\) = 3            b,\(x^2\) - 64  = 0

c,\(x^2\) + 16 = 25           d,|\(\sqrt{x}-3\)| + 3 = 9

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