解不等式 2y−1<11y4<142y - 1 < \frac{11y}{4} < \frac{1}{4}。 答案:... 已知 -25 ≤ x ≤ 50 且 -15 ≤ y ≤ -5,x + y^2 的最小可能值是多少? 答案:...

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完整解法

2(a)

1. Split the compound inequality into two inequalities.

2y−1<11y4and11y4<142y-1<\frac{11y}{4}\quad \text{and}\quad \frac{11y}{4}<\frac14

2. Solve the left inequality.

2y−1<11y42y-1<\frac{11y}{4}
Multiply by 44:
8y−4<11y8y-4<11y
−4<3y-4<3y
y>−43y>-\frac43

3. Solve the right inequality and combine both conditions.

11y4<14\frac{11y}{4}<\frac14
Multiply by 44:
11y<111y<1
y<111y<\frac{1}{11}

Combining with y>−43y>-\frac43 gives
−43<y<111.-\frac43<y<\frac{1}{11}.

答案

0<y<470<y<\dfrac{4}{7}

2(b)

1. Find the minimum possible values contributing to $x+y^2$.

Since −25≤x≤50-25\leq x\leq 50, the smallest possible value of xx is −25-25.

Since −15≤y≤−5-15\leq y\leq -5, the smallest possible value of y2y^2 occurs at y=−5y=-5:
y2=(−5)2=25.y^2=(-5)^2=25.

2. Calculate the smallest possible value of the expression.

Smallest possible value:
x+y2=−25+25=0.x+y^2=-25+25=0.

答案

00

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