8.NS.A.2: Approximating irrationals

Also written as 8.NS.2

Use rational approximations of irrational numbers to compare the size of irrational numbers, locate them approximately on a number line diagram, and estimate the value of expressions (e.g., π^2).

In plain words: Students estimate irrational numbers with rational ones to compare them, place them on a number line, and estimate expressions like π².

Quick picks

Example problem: Is $\sqrt{10}$ closer to $3.16$ or $3.17$ ?
Assign problem on Goblins →
Common mistake: Halving instead of taking the square root: √50 is a little more than 7, since 7² = 49, not about 25.
Builds on: 8.EE.A.2Square and cube roots 8.NS.A.1Irrational numbers

Example Problems

Is

\sqrt{10}

closer to

3.16

or

3.17

?

Is

-\sqrt{84}

closer to

-9.1

or

-9.2

?

Is

-\sqrt{50}

closer to

-7.0

or

-7.1

?

Khan Academy Resources

Approximating square roots walk through Approximating square roots Comparing irrational numbers with a calculator Comparing irrational numbers Approximating square roots to hundredths Comparing values with calculator Approximating square roots Comparing irrational numbers with radicals

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