【高校数学Ⅰ】2-1-2 二次関数のグラフ|問題集
1.次の二次関数のグラフをかき、頂点と軸を答えなさい。
(1)\(y=x^2+1\)
頂点:\((0,1)\)
軸:\(x=0\)
(2)\(y=2x^2-3\)
頂点:\((0,-3)\)
軸:\(x=0\)
(3)\(y=-x^2+2\)
頂点:\((0,2)\)
軸:\(x=0\)
(4)\(y=(x-2)^2\)
頂点:\((2,0)\)
軸:\(x=2\)
(5)\(y=2(x+1)^2\)
頂点:\((-1,0)\)
軸:\(x=-1\)
(6)\(y=-2(x+2)^2\)
頂点:\((-2,0)\)
軸:\(x=-2\)
(7)\(y=(x-1)^2+2\)
頂点:\((1,2)\)
軸:\(x=1\)
(8)\(y=2(x-2)^2-4\)
頂点:\((2,-4)\)
軸:\(x=2\)
(9)\(y=-2(x+1)^2+2\)
頂点:\((-1,2)\)
軸:\(x=-1\)
(10)\(\displaystyle y=-\frac{1}{2}(x+2)^2-1\)
頂点:\((-2,-1)\)
軸:\(x=-2\)
2.次の二次式を平方完成しなさい。
(1)\(y=x^2+8x\)
\(=x^2+8x+16-16\)
\(=(x+4)^2-16\)
\(=(x+4)^2-16\)
(2)\(y=x^2-6x+8\)
\(=x^2-6x+9-9+8\)
\(=(x-3)^2-1\)
\(=(x-3)^2-1\)
(3)\(2x^2+4x+5\)
\(=2(x^2+2x)+5\)
\(=2(x^2+2x+1-1)+5\)
\(=2(x+1)^2+3\)
\(=2(x^2+2x+1-1)+5\)
\(=2(x+1)^2+3\)
(4)\(y=3x^2-6x-2\)
\(=3(x^2-2x)-2\)
\(=3(x^2-2x+1-1)-2\)
\(=3(x-1)^2-5\)
\(=3(x^2-2x+1-1)-2\)
\(=3(x-1)^2-5\)
(5)\(y=x^2+x-2\)
\(\displaystyle =x^2+x+\frac{1}{4}-\frac{1}{4}-2\)
\(\displaystyle =\left(x+\frac{1}{2}\right)^2-\frac{9}{4}\)
\(\displaystyle =\left(x+\frac{1}{2}\right)^2-\frac{9}{4}\)
(6)\(y=-2x^2+6x+4\)
\(=-2(x^2-3x)+4\)
\(\displaystyle =-2\left(x^2-3x+\frac{9}{4}-\frac{9}{4}\right)+4\)
\(\displaystyle =-2\left(x-\frac{3}{2}\right)^2+\frac{17}{2}\)
\(\displaystyle =-2\left(x^2-3x+\frac{9}{4}-\frac{9}{4}\right)+4\)
\(\displaystyle =-2\left(x-\frac{3}{2}\right)^2+\frac{17}{2}\)
(7)\(y=2x^2+8x+10\)
\(=2(x^2+4x)+10\)
\(=2(x^2+4x+4-4)+10\)
\(=2(x+2)^2+2\)
\(=2(x^2+4x+4-4)+10\)
\(=2(x+2)^2+2\)
(8)\(y=3x^2+6x-10\)
\(=3(x^2+2x)-10\)
\(=3(x^2+2x+1-1)-10\)
\(=3(x+1)^2-13\)
\(=3(x^2+2x+1-1)-10\)
\(=3(x+1)^2-13\)
(9)\(y=-x^2-4x-1\)
\(=-(x^2+4x)-1\)
\(=-(x^2+4x+4-4)-1\)
\(=-(x+2)^2+3\)
\(=-(x^2+4x+4-4)-1\)
\(=-(x+2)^2+3\)
(10)\(y=-3x^2-9x+4\)
\(=-3(x^2+3x)+4\)
\(\displaystyle =-3\left(x^2+3x+\frac{9}{4}-\frac{9}{4}\right)+4\)
\(\displaystyle =-3\left(x+\frac{3}{2}\right)^2+\frac{43}{4}\)
\(\displaystyle =-3\left(x^2+3x+\frac{9}{4}-\frac{9}{4}\right)+4\)
\(\displaystyle =-3\left(x+\frac{3}{2}\right)^2+\frac{43}{4}\)
3.次の二次関数のグラフをかき、頂点と軸を答えなさい。
(1)\(y=x^2-4x+3\)
\(=x^2-4x+4-4+3\)
\(=(x-2)^2-1\)
頂点:\((2,-1)\)
軸:\(x=2\)
\(=(x-2)^2-1\)
頂点:\((2,-1)\)
軸:\(x=2\)
(2)\(y=2x^2+8x+3\)
\(=2(x^2+4x)+3\)
\(=2(x^2+4x+4-4)+3\)
\(=2(x+2)^2-5\)
頂点:\((-2,-5)\)
軸:\(x=-2\)
\(=2(x^2+4x+4-4)+3\)
\(=2(x+2)^2-5\)
頂点:\((-2,-5)\)
軸:\(x=-2\)
(3)\(y=-3x^2+6x+1\)
\(=-3(x^2-2x)+1\)
\(=-3(x^2-2x+1-1)+1\)
\(=-3(x-1)^2+4\)
頂点:\((1,4)\)
軸:\(x=1\)
\(=-3(x^2-2x+1-1)+1\)
\(=-3(x-1)^2+4\)
頂点:\((1,4)\)
軸:\(x=1\)
(4)\(y=-x^2+3x\)
\(=-(x^2-3x)\)
\(\displaystyle =-\left(x^2-3x+\frac{9}{4}-\frac{9}{4}\right)\)
\(\displaystyle =-\left(x-\frac{3}{2}\right)^2+\frac{9}{4}\)
頂点:\(\displaystyle \left(\frac{3}{2},\frac{9}{4}\right)\)
軸:\(\displaystyle x=\frac{3}{2}\)
\(\displaystyle =-\left(x^2-3x+\frac{9}{4}-\frac{9}{4}\right)\)
\(\displaystyle =-\left(x-\frac{3}{2}\right)^2+\frac{9}{4}\)
頂点:\(\displaystyle \left(\frac{3}{2},\frac{9}{4}\right)\)
軸:\(\displaystyle x=\frac{3}{2}\)
(5)\(y=-x^2+2x+1\)
\(=-(x^2-2x)+1\)
\(=-(x^2-2x+1-1)+1\)
\(=-(x-1)^2+2\)
頂点:\((1,2)\)
軸:\(x=1\)
\(=-(x^2-2x+1-1)+1\)
\(=-(x-1)^2+2\)
頂点:\((1,2)\)
軸:\(x=1\)
(6)\(y=-3x^2-2x+1\)
\(\displaystyle =-3\left(x^2+\frac{2}{3}x\right)+1\)
\(\displaystyle =-3\left(x^2+\frac{2}{3}x+\frac{1}{9}-\frac{1}{9}\right)+1\)
\(\displaystyle =-3\left(x+\frac{1}{3}\right)^2+\frac{4}{3}\)
頂点:\(\displaystyle \left(-\frac{1}{3},\frac{4}{3}\right)\)
軸:\(\displaystyle x=-\frac{1}{3}\)
\(\displaystyle =-3\left(x^2+\frac{2}{3}x+\frac{1}{9}-\frac{1}{9}\right)+1\)
\(\displaystyle =-3\left(x+\frac{1}{3}\right)^2+\frac{4}{3}\)
頂点:\(\displaystyle \left(-\frac{1}{3},\frac{4}{3}\right)\)
軸:\(\displaystyle x=-\frac{1}{3}\)
次の学習に進もう!