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Exercise 2.11 · Q5

Q.Find the radius of the spherical tank whose volume is 32π3\dfrac{32\pi}{3} cubic units.

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Concept understanding — Exponents and Radicals

Integer exponents. an=a⋅a⋯aa^n=a\cdot a\cdots a (nn times); a−m=1/ama^{-m}=1/a^m; aman=am+na^ma^n=a^{m+n}; am/an=am−na^m/a^n=a^{m-n}.

nnth roots (radicals). For nn even, b>0b>0 has a unique positive nnth root b1/nb^{1/n} (no real root exists for b<0b<0); for nn odd, every real bb has a unique real nnth root. n=2n=2 gives the square root, n=3n=3 the cube root. Crucially, a2=∣a∣\sqrt{a^2}=|a|, never plain aa -- more generally (an)1/n=∣a∣(a^n)^{1/n}=|a| if nn even, =a=a if nn odd.

Rational exponents. For a>0a>0 and r=m/nr=m/n (gcd⁡(m,n)=1\gcd(m,n)=1): am/n=(a1/n)ma^{m/n}=(a^{1/n})^m; all the integer-exponent laws extend to rational exponents wherever every term involved is actually defined (e.g. (−49)3/2(-49)^{3/2} is undefined in the reals, since (−49)1/2(-49)^{1/2} isn't real).

Simplifying compound radical/exponent expressions typically means rewriting every base as a perfect power of a common small integer (e.g. 125=53125=5^3, 256=28256=2^8, 27=3327=3^3) before applying the exponent laws, rather than computing large numbers directly. …

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