Concept

Multiplying Square Roots

The Product Property of Square Roots can be applied 'in reverse' to multiply two square roots: instead of splitting a single radical into a product of radicals, the property combines a product of radicals into a single radical. If aa and bb are nonnegative real numbers, then:

ab=ab\sqrt{a} \cdot \sqrt{b} = \sqrt{ab}

To multiply two square roots, place both radicands under a single radical sign and compute the product. For example, 35=35=15\sqrt{3} \cdot \sqrt{5} = \sqrt{3 \cdot 5} = \sqrt{15}. Sometimes the product inside the radical turns out to be a perfect square, in which case the radical simplifies to an integer — for instance, 28=16=4\sqrt{2} \cdot \sqrt{8} = \sqrt{16} = 4. When the product is not a perfect square, look for perfect-square factors in the result and simplify.

When the square roots have coefficients, multiply the coefficients together and multiply the radicands together — much like multiplying variables with coefficients. Just as 4x3y=12xy4x \cdot 3y = 12xy, the expression (4a)(3b)=12ab(4\sqrt{a})(3\sqrt{b}) = 12\sqrt{ab}. After multiplying, always check whether the resulting radical can be simplified further by extracting any perfect-square factors from the radicand. It is often easier to wait until after multiplying to simplify, rather than simplifying each radical beforehand.

These individual radical products also appear within polynomial multiplication when the factors contain square roots. The Distributive Property allows a single factor — whether a constant or a square root — to be distributed across a binomial that includes radicals; each resulting product is then simplified using the Product Property and any like radicals are combined. When two binomials containing square roots are multiplied, the FOIL method produces four products that are simplified and combined in the same way.

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Updated 2026-04-21

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