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To subtract these radicals together their radicands must be the same:

4\( \sqrt{63} \) - 2\( \sqrt{7} \)
4\( \sqrt{9 \times 7} \) - 2\( \sqrt{7} \)
4\( \sqrt{3^2 \times 7} \) - 2\( \sqrt{7} \)
(4)(3)\( \sqrt{7} \) - 2\( \sqrt{7} \)
12\( \sqrt{7} \) - 2\( \sqrt{7} \)

Now that the radicands are identical, you can subtract them:

A number in scientific notation has the format 0.000 x 10^exponent. To convert to scientific notation, move the decimal point to the right or the left until the number is a decimal between 1 and 10. The exponent of the 10 is the number of places you moved the decimal point and is positive if you moved the decimal point to the left and negative if you moved it to the right:

0.0000484 in scientific notation is 4.84 x 10^-5

To add or subtract terms with exponents, both the base and the exponent must be the same. In this case they are so add the coefficients and retain the base and exponent:

-3b⁴ + 1b⁴
(-3 + 1)b⁴
-2b⁴

The greatest common factor (GCF) is the greatest factor that divides two integers.