Используем формулы сокращенного умножения:
(a-b)(a+b)= a^2- b^2
(a+b)^2=a^2+2ab+b^2
(a-b)^2=a^2-2ab+b^2
а)![(x+\sqrt{y})(x-\sqrt{y})=x^{2} -y](https://tex.z-dn.net/?f=%28x%2B%5Csqrt%7By%7D%29%28x-%5Csqrt%7By%7D%29%3Dx%5E%7B2%7D+-y)
б)(![\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})=a-b](https://tex.z-dn.net/?f=%5Csqrt%7Ba%7D-%5Csqrt%7Bb%7D%29%28%5Csqrt%7Ba%7D%2B%5Csqrt%7Bb%7D%29%3Da-b)
в)(![\sqrt{11}-3)(\sqrt{11}+3)=11-9=2](https://tex.z-dn.net/?f=%5Csqrt%7B11%7D-3%29%28%5Csqrt%7B11%7D%2B3%29%3D11-9%3D2)
г)(![\sqrt{7}-\sqrt{10})(\sqrt{7}+\sqrt{10})= 7-10=-3](https://tex.z-dn.net/?f=%5Csqrt%7B7%7D-%5Csqrt%7B10%7D%29%28%5Csqrt%7B7%7D%2B%5Csqrt%7B10%7D%29%3D+7-10%3D-3)
д)![(\sqrt{a}+\sqrt{b} )^2=a+2 \sqrt{ab}+b](https://tex.z-dn.net/?f=%28%5Csqrt%7Ba%7D%2B%5Csqrt%7Bb%7D+%29%5E2%3Da%2B2+%5Csqrt%7Bab%7D%2Bb)
е)![(\sqrt{m} -\sqrt{n}) ^2=m-2\sqrt{mn}+n](https://tex.z-dn.net/?f=%28%5Csqrt%7Bm%7D+-%5Csqrt%7Bn%7D%29+%5E2%3Dm-2%5Csqrt%7Bmn%7D%2Bn)
ж)![(\sqrt{2}+3)^2=2+6\sqrt{2} +9=11+6\sqrt{2}](https://tex.z-dn.net/?f=%28%5Csqrt%7B2%7D%2B3%29%5E2%3D2%2B6%5Csqrt%7B2%7D+%2B9%3D11%2B6%5Csqrt%7B2%7D)
з)![(\sqrt{5} -\sqrt{2}) ^2=5-2\sqrt{5}\sqrt{2}+2=7-2\sqrt{10}](https://tex.z-dn.net/?f=%28%5Csqrt%7B5%7D+-%5Csqrt%7B2%7D%29+%5E2%3D5-2%5Csqrt%7B5%7D%5Csqrt%7B2%7D%2B2%3D7-2%5Csqrt%7B10%7D)
<span>(2a-b)(2a+b)+b^2=4a^2-b^2+b^2=4a^2</span>
<span><span>(x+7)^2-10x= x^2+14x+49-10x=x^2+4x+49</span></span>
<span><span><span>9x^2 - (c+3x)(c-3x)=9x^2-(c^2-9x^2)=9x^2-c^2+9x^2=18x^2-c^2</span></span></span>
<span><span><span><span>5b^2-(a-2b)^2=5b^2-(a^2-4ab-4b^2)=5b^2-a^2+4ab+4b^2=9b^2-a^2+4ab</span></span></span></span>
У= 5*3,6:4
у=4,5
крест на крест
An=a1+(n-1)d
An= 2+(n-1)*(-0,8)
An=2-0,8n+0,8
An=2,8-0,8n
A11=...