Tính hợp lí:
E = (144 x 790) : 72
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\(36\text{×}5+72\text{×}2-216+144\)
\(=36\text{×}5+36\text{×}2\text{×}2-36\text{×}6+36\text{×}4\)
\(=36\text{×}5+36\text{×}4-36\text{×}6+36\text{×}4\)
\(=36\text{×}\left(5+4-6+4\right)=36\text{×}7=252\)
`= 72 xx 19 + 36 xx 2 xx3 xx 10 + 72 xx 80 - 72 xx 29`
`= 72 xx(19 + 30 - 29 + 80)`
`= 72 xx 100`
`= 7200`
\(=72.19+36.2.3.10+72.2.40-72.29\)
\(=72.19+72.30+72.80-72.29\)
\(=72.\left(19+30+80-29\right)\)
\(=72.100=7200\)
a) \(96-7\left(x+1\right)=14^4:14^3\)
\(\Rightarrow96-7\left(x+1\right)=14^{4-3}\)
\(\Rightarrow96-7\left(x+1\right)=14\)
\(\Rightarrow7\left(x+1\right)=96-14\)
\(\Rightarrow7\left(x+1\right)=82\)
\(\Rightarrow x+1=\dfrac{82}{7}\)
\(\Rightarrow x=\dfrac{82}{7}-1\)
\(\Rightarrow x=\dfrac{75}{7}\)
b) \(\left(5x+3^4\right)\cdot2^4=2^6\cdot7^2\)
\(\Rightarrow5x\cdot2^4+3^4\cdot2^4=2^6\cdot7^2\)
\(\Rightarrow5x\cdot2^4+6^4=\left(2^3\cdot7\right)^2\)
\(\Rightarrow80x+1296=3136\)
\(\Rightarrow80x=1840\)
\(\Rightarrow x=\dfrac{1840}{80}\)
\(\Rightarrow x=23\)
a: =>96-7(x+1)=14
=>7(x+1)=82
=>x+1=82/7
=>x=75/7
b =>5x+81=2^2*7^2=196
=>5x=115
=>x=23
\(72^2+144\cdot16+16^2-12^2\)
\(=\left(72^2+144\cdot16+16^2\right)-12^2\)
\(=\left(72^2+2\cdot72\cdot16+16^2\right)-12^2\)
\(=\left(72+16\right)^2-12^2\)
\(=88^2-12^2\)
\(=\left(88+12\right)\left(88-12\right)\)
\(=100\cdot76\)
\(=7600\)
E = ( 144 x 790 ) : 72
= 144 x 790 : 72
= ( 144 : 72 ) x 790
= 2 x 790
= 1580