Tangent (π- α) × cos (-π/2 +α) > 0. the answer is that cos α < 0. i forgot to put the negative sign. how do i solve this? does this method also applies to sen(-π/2-α). i get confused when i see questions like these.

The u-drive rent-a-truck company plans to spend $13 million on 320 new vehicles. each commercial van will cost $25 comma 000, each small truck $50 comma 000, and each large truck  $80 comma 000. past experience shows that they need twice as many vans as small trucks. how many of each type of vehicle can they buy?

Geometry in the diagram, ∠abc is a right angle. ∠dbc = 30°27'40". find the measure of ∠abd.

What is the slope of the line shown below?