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For many people, learning trigonometric functions seems meaningless.
Literal
Many [genitive-の] people [for-にとって] trigonometric-functions [object-を] learning [topic-は] meaningless [literary-copula-である] [manner-ように] seems.
A philosophical take on math education. 三角関数 ('trigonometric functions') is a Sino-Japanese compound: 三角 (triangle) + 関数 (function). The frame ~にとって marks the perspective holder ('for X'). 無意味である uses the literary copula である with a な-adjective-like noun. ~ように思える ('seems like / appears to be') is a softer, more hedged version of ~と思う — presenting the view as an external appearance rather than the speaker's firm opinion.