Question

Rút gọn biểu thức:

A= \(\frac{1}{a^2-5a+6}+\frac{1}{a^2-7a+12}+\frac{1}{a^2-9a+20}\)

Answer 1

Để mk giải cho

Answer 2

\(\frac{3}{\left(a-2\right)\left(a-3\right)}\). minh khong chac dau nha. neu sai thi thoi.

Answer 3

theo đề ta có :

A= (1 /a² - 2a -3a + 6) + ( 1 /a² -3a -4a + 12 ) + ( 1 /a² - 4a -5a + 20 )

\(\Leftrightarrow\) A = (1 /( a -2 )(a-3 ))+ (1/(a-3)(a-4))+(1/(a-4)(a-5)).

\(\Leftrightarrow\)A = (1/a-2) - (1/ a-3) +(1/ a-3) -(1/ a-4) +(1/ a-4) - (1/ a-5)

\(\Leftrightarrow\)A = (1/a-2) - (1/ a-5)

\(\Leftrightarrow\)A = a-5-a+2 / (a-2)(a-5)

\(\Leftrightarrow\)A= 3 / ( a -2 )(a-5)

chúc bạn học tốt

Answer 4

\(\frac{3}{\left(a-2\right)\left(a-5\right)}\)

Answer 5

Ta có :A=\(\frac{1}{a^2-5a+6}\)+\(\frac{1}{a^2-7a+12}\)+ \(\frac{1}{a^2-9a+20}\)

A=\(\frac{1}{\left(a-2\right)\left(a-3\right)}\)+ \(\frac{1}{\left(a-3\right)\left(a-4\right)}\)+\(\frac{1}{\left(a-4\right)\left(a-5\right)}\)= \(\frac{1}{a-2}\)-\(\frac{1}{a-3}\)+\(\frac{1}{a-3}\)- \(\frac{1}{a-4}\)+\(\frac{1}{a-4}\)-\(\frac{1}{a-5}\)

A = \(\frac{1}{a-2}\)- \(\frac{1}{a-5}\)= \(\frac{a-5}{\left(a-2\right)\left(a-5\right)}\)- \(\frac{a-2}{\left(a-5\right)\left(a-2\right)}\)= \(\frac{a-5-a+2}{\left(a-2\right)\left(a-5\right)}\)=\(\frac{-3}{\left(a-2\right)\left(a-5\right)}\)

vậy biểu thức rút gọn A=\(\frac{-3}{\left(a-2\right)\left(a-5\right)}\)

Answer 6

mk xl , mk thiếu đkxđ a khác 2;3;4;5

Answer 7

\(\frac{1}{\left(a-5\right)}-\frac{1}{\left(a-2\right)}\)

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