Titik minimum dari fungsi trigonometri [tex]y=-15cos(x+ \frac{1}{4} \pi ), 0\ \textless \ x\ \textless \ 2 \pi [/tex]

y = - 15 cos (x+ ¹/₄π)
cos (x + ¹/₄ π)= 1
cos (x + 1/4 π) = cos 0 ---> x = - 1/4 π (TM)
cos (x + 1/4 π)= cos 2π --> x = 7π/4 (memenuhi)  ->0 < x  < 2π

y = -15 (1) = - 15

titk  minimum (x,y) = (⁷/₄ π, -17)