分别在不同的图上,在数轴上表示以下不等式的解集:

  1. ((i))

    3(5−x)>x+133(5 - x) > x + 13

  2. ((ii))

    x2−12x<14(3−2x)x^{2} - \frac{1}{2}x < \frac{1}{4}(3 - 2x)

  3. ((iii))

    写出同时满足这两个不等式的 x 的取值集合。

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完整解法

b((i))

1. Expand the left-hand side and simplify the inequality.

3(5−x)>x+133(5-x)>x+13

15−3x>x+1315-3x>x+13

2. Collect like terms and solve for $x$.

15−3x>x+1315-3x>x+13

15−13>x+3x15-13>x+3x

2>4x2>4x

x<12x<\dfrac{1}{2}

3. Represent the solution set on the number line.

Since x<12x<\dfrac{1}{2}, draw an open circle at 12\dfrac{1}{2} and shade the number line to the left.

答案

x<12x<\dfrac{1}{2}

On the number line: open circle at 12\dfrac{1}{2}, shaded to the left.

b((ii))

1. Clear fractions and collect all terms on one side.

x2−12x<14(3−2x)x^{2}-\dfrac{1}{2}x<\dfrac{1}{4}(3-2x)

Multiply throughout by 44:

4x2−2x<3−2x4x^{2}-2x<3-2x

Add 2x2x to both sides:

4x2<34x^{2}<3

4x2−3<04x^{2}-3<0

2. Factorise the quadratic expression using difference of squares.

4x2−3<04x^{2}-3<0

(2x)2−(3)2<0(2x)^{2}-(\sqrt{3})^{2}<0

(2x−3)(2x+3)<0(2x-\sqrt{3})(2x+\sqrt{3})<0

3. Determine the interval where the quadratic expression is negative and represent it on the number line.

Critical values:

2x−3=0⇒x=322x-\sqrt{3}=0 \Rightarrow x=\dfrac{\sqrt{3}}{2}

2x+3=0⇒x=−322x+\sqrt{3}=0 \Rightarrow x=-\dfrac{\sqrt{3}}{2}

Since 4x2−3<04x^{2}-3<0, the quadratic is below 00 between the two roots.

Therefore,

−32<x<32-\dfrac{\sqrt{3}}{2}<x<\dfrac{\sqrt{3}}{2}

答案

−12<x<32-\dfrac{1}{2}<x<\dfrac{3}{2}

On the number line: open circles at −12-\dfrac{1}{2} and 32\dfrac{3}{2}, shaded between them.

b((iii))

1. Find the overlap of the two solution sets from parts (i) and (ii).

From (i), x<12x<\dfrac{1}{2}.

From (ii), −12<x<32-\dfrac{1}{2}<x<\dfrac{3}{2}.

The values satisfying both are the common values:

−12<x<12-\dfrac{1}{2}<x<\dfrac{1}{2}

答案

−12<x<12-\dfrac{1}{2}<x<\dfrac{1}{2}

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