What is the value of 2.5*cos(30) ?

The value of 2.5*cos(30) is (5sqrt(3))/4

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2.5*cos(30)

2.5 \cdot cos (3 0^{\circ})

\frac{5 3}{4}

Decimal

2.16506 \dots

Solution steps

2.5 cos (3 0^{\circ})

= \frac{5}{2} cos (3 0^{\circ})

Use the following trivial identity:

cos (3 0^{\circ}) = \frac{3}{2}

cos (3 0^{\circ})

cos (x)

periodicity table with

36 0^{\circ} n

cycle:

x 0 3 0^{\circ} 4 5^{\circ} 6 0^{\circ} 9 0^{\circ} 12 0^{\circ} 13 5^{\circ} 15 0^{\circ} cos (x) 1 \frac{3}{2} \frac{2}{2} \frac{1}{2} 0 - \frac{1}{2} - \frac{2}{2} - \frac{3}{2} x 18 0^{\circ} 21 0^{\circ} 22 5^{\circ} 24 0^{\circ} 27 0^{\circ} 30 0^{\circ} 31 5^{\circ} 33 0^{\circ} cos (x) - 1 - \frac{3}{2} - \frac{2}{2} - \frac{1}{2} 0 \frac{1}{2} \frac{2}{2} \frac{3}{2}

= \frac{3}{2}

= \frac{5}{2} \cdot \frac{3}{2}

Simplify

\frac{5}{2} \cdot \frac{3}{2} : \frac{5 3}{4}

\frac{5}{2} \cdot \frac{3}{2}

Multiply fractions:

\frac{a}{b} \cdot \frac{c}{d} = \frac{a \cdot c}{b \cdot d}

= \frac{5 3}{2 \cdot 2}

Multiply the numbers:

2 \cdot 2 = 4

= \frac{5 3}{4}

= \frac{5 3}{4}