48:6=8 кг-один ящик с печеньем
8+3=11 кг-один ящик с конфетами
11*8=88 кг
1) x^2 + 4x<span> - 21 = 0
D = </span>4^2<span> - 4·1·(-21) = 16 + 84 = 100
</span>x1 = (<span><span>-4 - √100)/</span>2·1</span> = (<span>-4 - 10)/2</span> = <span>-14/2</span><span> = -7
</span>x2 = (<span><span>-4 + √100)/</span>2·1</span> = (<span>-4 + 10)/2</span> = <span>6/2</span><span> = 3
</span>2) 2x^2 + 10x<span> = 0
</span>D = 10^2<span> - 4·2·0 = 100 - 0 = 100
</span>x1 = (<span><span>-10 - √100)/</span>2·2</span> = (<span>-10 - 10)/4</span> = <span>-20/4</span><span> = -5
</span>x2 = (<span><span>-10 + √100)/</span>2·2</span> = (<span>-10 + 10)/4</span> = <span>0/4</span><span> = 0
</span>3) x^2 + 3x<span> - 18 = 0
</span>D = 3^2<span> - 4·1·(-18) = 9 + 72 = 81
</span>x1 = (<span><span>-3 - √81)/</span>2·1</span> = (<span>-3 - 9)/2</span> = <span>-12/2</span><span> = -6
</span>x2 = (<span><span>-3 + √81)/</span>2·1</span> = (<span>-3 + 9)/2</span> = <span>6/2</span><span> = 3
</span>4) 5x^2 + 15x<span> = 0
</span>D = 15^2<span> - 4·5·0 = 225 - 0 = 225
</span>x1 = (<span><span>-15 - √225)/</span>2·5</span> = (<span>-15 - 15)/10</span> = <span>-30/10</span><span> = -3
</span>x2 = (<span><span>-15 + √225)/</span>2·5</span> = (<span>-15 + 15)/10</span> = <span>0/10</span><span> = 0</span>
<span>5) x = -20
</span>
№ 1. 4 1/7 + 12 + 3 5/14 = 19 1/2
1) 4 1/7 + 12 = 16 1/7
2) 16 1/7 + 3 5/14 = 16 2/14 + 3 5/14 = 19 7/14 = 19 1/2
№ 2. (4,5 * 100) : (9 : 100) = 5 000
1) 4,5 * 100 = 450
2) 9 : 100 = 0,09
3) 450 : 0,09 = 5 000
Слева и справа должна быть одна и та же цифра - 1101, 2102, 3103, 4104 и т.д.