15xy − 5x + 18y − 6; если x= −0,9, а y = 1 1/3 или 4/3
1) 15×(-0,9)×4/3 = -13,5×4/3 = -54/3 = -18
2) -18 - 5×(-0,9) = -18 + 4,5 = -13,5
3) -13,5 + 18 × 4/3 = -13,5 + 72/3 = -13,5 + 24 = 10,5
4) 10,5 - 6 = 4,5
1) ![(m-n)(m+3)=m\cdot m+3\cdot m-m\cdot n-3\cdot n=m^{2}+3m-mn-3n](https://tex.z-dn.net/?f=%28m-n%29%28m%2B3%29%3Dm%5Ccdot%20m%2B3%5Ccdot%20m-m%5Ccdot%20n-3%5Ccdot%20n%3Dm%5E%7B2%7D%2B3m-mn-3n)
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2) ![(4+5a)(5a-4)=4\cdot5a-4\cdot4+5a\cdot5a-4\cdot5a=20a-16+25a^{2}-20a=25a^{2}+(20a-20a)-16=25a^{2}-16](https://tex.z-dn.net/?f=%284%2B5a%29%285a-4%29%3D4%5Ccdot5a-4%5Ccdot4%2B5a%5Ccdot5a-4%5Ccdot5a%3D20a-16%2B25a%5E%7B2%7D-20a%3D25a%5E%7B2%7D%2B%2820a-20a%29-16%3D25a%5E%7B2%7D-16)
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3) ![(8b+5a)(5a-8b)=5a\cdot8b-8b\cdot8b+5a\cdot5a-5a\cdot8b=40ab-64b^{2}+25a^{2}-40ab= 25a^{2}+(40ab-40ab)-64b^{2}=25a^{2}-64b^{2}](https://tex.z-dn.net/?f=%288b%2B5a%29%285a-8b%29%3D5a%5Ccdot8b-8b%5Ccdot8b%2B5a%5Ccdot5a-5a%5Ccdot8b%3D40ab-64b%5E%7B2%7D%2B25a%5E%7B2%7D-40ab%3D%2025a%5E%7B2%7D%2B%2840ab-40ab%29-64b%5E%7B2%7D%3D25a%5E%7B2%7D-64b%5E%7B2%7D)
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4) ![(c-7)(c+7)=c\cdot c+7\cdot c-7\cdot c-7\cdot7=c^{2}+7c-7c-49=c^{2}+(7c-7c)-49=c^{2}-49](https://tex.z-dn.net/?f=%28c-7%29%28c%2B7%29%3Dc%5Ccdot%20c%2B7%5Ccdot%20c-7%5Ccdot%20c-7%5Ccdot7%3Dc%5E%7B2%7D%2B7c-7c-49%3Dc%5E%7B2%7D%2B%287c-7c%29-49%3Dc%5E%7B2%7D-49)
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5) ![(7x-2)(7x+2)=7x\cdot7x+2\cdot7x-2\cdot7x-2\cdot2=49x^{2}+14x-14x-4=49x^{2}+(14x-14x)-4= 49x^{2}-4](https://tex.z-dn.net/?f=%287x-2%29%287x%2B2%29%3D7x%5Ccdot7x%2B2%5Ccdot7x-2%5Ccdot7x-2%5Ccdot2%3D49x%5E%7B2%7D%2B14x-14x-4%3D49x%5E%7B2%7D%2B%2814x-14x%29-4%3D%2049x%5E%7B2%7D-4)
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6) ![(10p-6q)(10p+6q)=10p\cdot10p+10p\cdot6q-10p\cdot6q-6q\cdot6q=100p^{2}+60pq-60pq-36q^{2}=100p^{2}+(60pq-60pq)-36q^{2}=100p^{2}-36q^{2}](https://tex.z-dn.net/?f=%2810p-6q%29%2810p%2B6q%29%3D10p%5Ccdot10p%2B10p%5Ccdot6q-10p%5Ccdot6q-6q%5Ccdot6q%3D100p%5E%7B2%7D%2B60pq-60pq-36q%5E%7B2%7D%3D100p%5E%7B2%7D%2B%2860pq-60pq%29-36q%5E%7B2%7D%3D100p%5E%7B2%7D-36q%5E%7B2%7D)
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Обозначим числа как х и y.
x+y=170⇒y=170-x
0,6*x+0,7*y=110⇒0,6*x+0,7*(170-x)=110⇒0,6*x+119-0,7*x=110⇒-0,1*x=-9⇒x=90, тогда y=170-90=80.
Проверка: 80+90=170-верно!
0,6*90+0,7*80=54+56=110 - верно!
Ответ: 90 и 80.
1 x1=1 x2=-1
2 x1=7 x2=-7
3 a2-36
4 m2-64
5 x2-10x+25
6 81m2+6mn+1/9n2
9 x=4 (x-4)2=0 x-4=0 x=4 так же можно через дискриминант