解方程习题PPT
习题一解方程:$2x - 5 = 3x + 2$解:将所有项移到方程的一边得到:$2x - 3x = 2 + 5$合并同类项得到:$-x = 7$系数化为...
习题一解方程:$2x - 5 = 3x + 2$解:将所有项移到方程的一边得到:$2x - 3x = 2 + 5$合并同类项得到:$-x = 7$系数化为1得到:$x = -7$习题二解方程:$\frac{x}{2} + 1 = \frac{3x - 1}{4}$解:消去分母两边同时乘以4(最小公倍数),得到:$2x + 4 = 3x - 1$将所有项移到方程的一边得到:$2x - 3x = -1 - 4$合并同类项得到:$-x = -5$系数化为1得到:$x = 5$习题三解方程:$x^2 - 4x - 5 = 0$解:对方程进行因式分解得到:$(x - 5)(x + 1) = 0$根据因式分解的结果得到两个方程:$x - 5 = 0$ 或 $x + 1 = 0$分别解这两个方程得到:$x_1 = 5$,$x_2 = -1$习题四解方程:$3x^2 - 2x - 1 = 0$(使用求根公式)解:确定系数$a = 3$,$b = -2$,$c = -1$计算判别式$\Delta = b^2 - 4ac = (-2)^2 - 4 \times 3 \times (-1) = 4 + 12 = 16$使用求根公式计算$x$的值$x = \frac{-b \pm \sqrt{\Delta}}{2a} = \frac{2 \pm \sqrt{16}}{6} = \frac{2 \pm 4}{6}$得到两个解$x_1 = \frac{2 + 4}{6} = 1$$x_2 = \frac{2 - 4}{6} = -\frac{1}{3}$习题五解方程组:$\left{\begin{array}{l}2x + y = 5 \x - 2y = 4 \\end{array}\right.$解:使用加减消元法将第一个方程乘以2后与第二个方程相加,得到:$2(2x + y) + (x - 2y) = 5 \times 2 + 4$$5x = 14$$x = \frac{14}{5}$将$x = \frac{14}{5}$代入第一个方程得到:$2 \times \frac{14}{5} + y = 5$$\frac{28}{5} + y = 5$$y = 5 - \frac{28}{5}$$y = \frac{25 - 28}{5}$$y = -\frac{3}{5}$因此,方程组的解为:$\left{\begin{array}{l}x = \frac{14}{5} \y = -\frac{3}{5} \\end{array}\right.$习题六解方程组:$\left{\begin{array}{l}\frac{x}{2} + \frac{y}{3} = 5 \3x - 2y = 12 \\end{array}\right.$解:对方程组进行去分母处理得到:$\left{\begin{array}{l}3x + 2y = 30 \quad (①) \3x - 2y = 12 \quad (②) \\end{array}\right.$使用加减消元法将方程(①)与方程(②)相加,得到:$3x + 2y + 3x - 2y = 30 + 12$$6x = 42$$x = 7$将$x = 7$代入方程(②)得到:$3 \times 7 - 2y = 12$$21 - 2y = 12$$-2y = 12 - 21$$-2y = -9$$y = \frac{9}{2}$因此,方程组的解为:$\left{\begin{array}{l}x = 7 \y = \frac{9}{2} \\end{array}\right.$习题七解方程组:$\left{\begin{array}{l}x + y + z = 6 \quad (①) \x - y + z = 2 \quad (②) \x + 2y + 3z = 16 \quad (③) \\end{array}\right.$解:使用加减消元法将方程(①)与方程(②)相加,得到:$2x + 2z = 8$$x + z = 4$$z = 4 - x \quad (④)$将方程(④)代入方程(①)得到:$x + y + 4 - x = 6$$y = 2 \quad (⑤)$将方程(④)和方程(⑤)代入方程(③)得到:$x + 2 \times 2 + 3(4 - x) = 16$$x + 4 + 12 - 3x = 16$$-2x = 16 - 16$$-2x = 0$$x = 0$将$x = 0$和$y = 2$代入方程(④)得到:$z = 4 - 0$$z = 4$因此,方程组的解为:$\left{\begin{array}{l}x = 0 \y = 2 \z = 4 \\end{array}\right.$习题八解方程组:$\left{\begin{array}{l}\frac{x}{2} + y + z = 10 \quad (①) \x + \frac{y}{3} + z = 12 \quad (②) \x + y + \frac{z}{2} = 14 \quad (③) \\end{array}\right.$解:对方程组进行去分母处理得到:$\left{\begin{array}{l}3x + 6y + 6z = 60 \quad (④) \6x + 2y + 6z = 72 \quad (⑤) \2x + 2y + 3z = 28 \quad (⑥) \\end{array}\right.$使用加减消元法将方程(④)与方程(⑤)相减,得到:$3x - 6x + 6y - 2y + 6z - 6z = 60 - 72$$-3x + 4y = -12$$x - \frac{4}{3}y = 4 \quad (⑦)$将方程(⑦)乘以2后与方程(⑥)相加得到:$2(x - \frac{4}{3}y) + 2x + 2y + 3z = 2 \times 4 + 28$$2x - \frac{8}{3}y + 2x + 2y + 3z = 8 + 28$$4x - \frac{2}{3}y + 3z = 36 \quad (⑧)$将方程(⑦)乘以3后与方程(⑧)相加得到:$3(x - \frac{4}{3}y) + 4x - \frac{2}{3}y + 3z = 3 \times 4 + 36$$3x -