C. Much easier to build than a refracting telescopeBig mirrors used in mirroring telescopes are easier and also cheaper to do than large lenses which would cost much more because that the top quality of glass forced to make refracting telescopes

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Suppose the the terminal rate of a specific sky diver is 165 km/h in the spread-eagle position and also 320 km/h in the nosedive

3.76

Explanation:

We are offered that

Terminal speed in the spread -eagle position, Terminal speed in the nosedive position, We have to discover the proportion of the efficient cross-sectional area A in the slower position to the in the faster position.

We recognize that

Area, A=      1) Well, we recognize that lens is make by using 2 concave or convex winter or sometimes we also use one airplane mirror. The spherical winter are component of the glass sphere, and also hence they have actually a centre and corresponding radius.

2F is double of focal size when irradiate passes native one surface ar to one more of the lens, so it deserve to be claimed as the centre of curvature of the one of those spherical lens.

2) Distance in between the optical centre and the center of curvature is a lens have the right to be termed as the radius of curvature the the lens. Well, us don"t generally use these in instance of lens. But still, the distance in between O and also 2F is dual of the focal length or radius of curvature.

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The frequency is Explanation:

For a routine motion:

The period (T) of the movement is the moment it takes for the human body to make one complete oscillation.The frequency (f) the the movement is the number of complete oscillations make in one second

Frequency and period are associated by the equation: where

f is the frequency

T is the period

For the activity in this problem, we have: is the period

Therefore, the frequency is: brainly.com/question/5354733

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derekwadsworth.com: C. Binary star systemsLet’s watch your options:a) The color of the star: the color is not used in calculating the massive of a star, because it has no relationship to it. Think around a red supergiant and a red dwarf: they have the same color, however they are totally different stars, v respectively a big and a small mass.b) Kepler’s laws: these laws can be applied in what is referred to as the “approximation the 1 body”, which way that is assumed that one body has a much bigger mass 보다 the other and also can be thought about at rest. This is the case of a star-planet system and the massive that can be calculate is the of the planet.c) Binary star systems: these space the only situations in which is possible the straight measure of the massive of the stars. Binary systems room classified as follows:- visual binaries: every star can be resolved and the motion about the facility of mass can be measured.- Astrometric binaries: just one star is visible, however the visibility of the companion can be inferred through the activity of the very first star approximately the system’s facility of mass.- Eclipse binaries: the two stars are not solved (separated), but the luminosity varies periodically when one star eclipses the other.- Spectroscopic binaries: the 2 stars room not resolved, but their spectrum reveals that they space a binary system.In all these instances we have actually a “two-body problem” that have the right to be addressed by changing system the reference: the movement of body 1 and 2 is indistinguishable to the activity of a body of mass same to the system’s lessened mass moving in the potential produced by the total mass (M1 + M2) considered at rest. Hence, we can determine the masses that the 2 stars.