-3.1+(2.8+(-0.9))= -3.1+1.9= -1.2
(-2 3/7+5 1/14)+(-3.2)= (-17/7+71/14)+(-3.2)=((-34+71)/14)+(-3.2)=37/14+(-3.2)=37/14-3 1/5=37/14-16/5=(185-224)/70= -39/70
209/209 = 209 : 209 = 1
75/3 = 75 : 3 = 25
Парабола ветви вверх так как а>0
вершина в точке
2х-4=0
х=4/2=2
у=2²-4*2-5=4-8-5=-6
пересечение с осью х (у=0)
х²-4х-5=0
<span><span>D=<span><span>b2</span>−<span><span>4a</span>c</span></span></span>=</span><span><span><span><span><span>(<span>−4</span>)</span>2</span>−<span><span>4·1</span>·<span>(<span>−5</span>)</span></span></span>=<span>16+20</span></span>=36</span>
<span>(<span>D>0</span>)</span>, следовательно это квадратное уравнение имеет 2 различных вещественных корня:
Вычислим корни:
<span><span>x<span>(<span>1,2</span>)</span></span>=<span><span><span>−b</span>±√D</span><span>/2a
</span></span></span><span><span><span><span>x1=<span><span><span>−b</span>+√D/</span><span>2a</span></span></span>=<span><span><span>−<span>(<span>−4</span>)</span></span>+6/</span><span>2·1</span></span></span>=<span>10/2</span></span>=5
</span><span><span><span><span>x2=<span><span><span>−b</span>−√D</span><span>/2a</span></span></span>=<span><span><span>−<span>(<span>−4</span>)</span></span>−6</span><span>/2·1</span></span></span>=<span><span>−2/</span>2</span></span>=<span>−1</span></span>
<span><span>x1</span>=5</span>
<span><span>x2</span>=<span>−<span>1
таблица точек
</span></span></span>х у
<span><span>-4 27</span><span>
-3 16</span><span>
-2 7</span><span>
-1 0
</span><span>0 -5
</span><span>1 -8</span><span>
2 -9</span><span>
3 -8</span><span>
4 -5</span><span>
5 0</span><span>
6 7
</span><span>7 16</span><span>
8 27</span></span>
13-7=6(карандашей)
Ответ:6 карандашей синего цвета.
648-х=529 357+у=640 4*а=836 с:7=126
х= 648-529 у= 640-357 а= 836:4 с=126*7
х= 119 у= 283 а=209 с=882
