What is cos θ if sin θ = −8/10 and θ is in Quadrant III?

Drawing out the quadrants cos of an angle is negative in the third quadrant. Your drawing should indicate that x and y are negative. Then since we  are working with a right triangle, again your diagram should indicate that. Determine the value of the third side. You know one is - 6 and the other opposite the 90 degree angle, the hypotenuse is 10.   cos of an angle is adjacent divided by the hypotenuse.

I hope this helps if it did not help use this

cosine is negative in Quadrant III.

Use a pythagorean theorem to find the other leg.  a2 = c2 - b2

adjacent leg = √(102 - 82)

cos θ = -6/10

step-by-step explanation:

we can use this expression to calculate the energy gain as a particle moves with a field or the energy loss as it moves against it. (note that it is also used to define the electron-volt, a unit of energy equal to that gained by an electron as it falls through a pd of 1 v, i.e. w = 1 ev = 1.6 10-19 c 1 v = 1.6 10-19j).in fact this expression is really nothing more than the statement that potential is the potential energy per unit charge. in this case, v= w/qis simply stating that the change in potential energy(or work done) per unit charge is equal to the change in potential (or potential difference), v.student questions: uniform electric fields2electron beamcathode+5 kvanode0 v